Lynn, you were born to be a librarian–that inherent need to put things in order is a sign! 
Another thing: I assume that most cities and/or counties these days allow you to take a book out at any library and return it to any library. You’d be amazed at how many of these books never find their way back to the originating library.
And they are very hard to find on a shelf. If they are in the correct place, no one will think to open the book to look inside for the library stamp unless a deliberate trace for the missing copy has been sent throughout the system.
Well, REALLY you should dump it on a table, reshelving cart, hell, even a clean floor might be preferable because then it will be picked up. We looove it when you bring it to the desk, because then we get to say “Hmm, is it on the missing list?” If you really can’t be bothered, however, putting it paper up just makes it more noticeable that it’s not like that because it’s too tall or is in some other way supposed to be there.
Eventually they may find the missing book.
A couple of years ago, a nearby library did a major building redo and removed all books, shelves and equipment. A letter postmarked in WWII was found. The building had been a postoffice decades earlier.
Of course, some books are notoriously missing. I once needed a reference work urgently. I checked the online catalog, saw it listed as available. Walked 15 minutes in heavy snow to the concerned department library. Didn’t find the book at its catalogued location. Out of desperation, looked through the entire shelf, in case anyone had genuinely misshelved it. Rearranged the initial call numbers and looked there as well (641 -> 146 & 461…etc). No luck. Note there weren’t any students in the limited reading areas of the library. Probably spent 20 minutes searching. Walked back home. 90 minutes later, I check the catalog again and it’s checked out.
Which probably means that someone else needed it, too (possibly for the same reasons as you), spent 30 seconds seeing if it was where it was supposed to be, and then, while you were performing your heroic search, asked a librarian :).
I’ve filled out plenty of missing forms ere & since, but have always been told to come back the next morning. Maybe the lucky patron sweet-talked the librarian into doing an instant search.
Another librarian checking in. (Large public library system, but have also worked in an academic library.) As some people have previously stated, there are several possibilities why a book wouldn’t be located where it should be.
It could be misfiled, most likely by a browsing patron who put the book back in the wrong place. When looking for a missing book, I always skim through the shelves nearby to see if I can spot it.
It could be deliberately hidden within the library, so that the patron can always come in an consult it, without checking it out. This tends to happen much more frequently in academic libraries.
It could have been stolen, sadly. If we see a book that hasn’t been checked out in the best part of a year (or more), we do not expect to be able to find that book on the shelves. Although we do always look, of course, and sometimes get lucky.
Someone could be walking around with it. This is only likely in the case of popular new titles or school assignment books.
Finally – and this is why you should always double check with a librarian – we could be keeping it in the back, in “overflow”. Sometimes when shelf space is tight, we will keep some of the materials on shelves in the back until either someone asks for it (in which case we’ll run back and grab it for them), or we have time to free up enough space in the section to bring out the overflow.
Librarians can often guess which of the above situations it is likely to be, from the date that the book was last returned. If it only just came back, for example, it could be one of those books that wouldn’t fit out on the shelves and got put back in overflow. If it hasn’t been checked out for a year, it has probably been stolen. In my library system we get rid of books that haven’t been checked out a few times a year on average (unless there is a good reason to keep them). If a book hasn’t been checked out for at least 18 months, and hasn’t been weeded (mostly likely because we couldn’t find it to physically get rid of it), it will be purged from the catalog.
We have circulation assistants (CA’s) – mostly teens, but not all – who do shelf-reading as well as shelving and helping at the check-out desk. They are required to read (i.e. put books in order) for at least 15 minutes per shift. I would expect a misfiled book to be located and put back in its proper position within a few weeks in a library of our size (about 100,000 items). I’m working for a relatively small library in the system; in our biggest libraries it could take up to a couple of months for a CA to come across the book and shelve it properly.
If you are a patron and see a book out of order, I encourage you to take it off the shelf and leave it on a table. We will eventually notice a book that is turned sideways, but we will quickly notice a book that is left lying around on a table – these are cleaned up and reshelved several times throughout the day.
I have often wondered why libraries don’t put their bar codes on the spines of the books (instead of inside the flap or on the back cover).
If they did this (with the bars perpindicular to the spine), a worker could take a portable RF scanner terminal, scan a shelf number (presumably displayed prominantly on the front of the shelf) and then proceed to scan the books, left-to-right, across the shelf. Besides providing a solid physical inventory, the gun could beep whenever it finds a book out of place.
I think that a library worker could do dozens of shelves in a short time using such a setup.
In my workplace, we use such a system to track hundreds of thousands of odd little chemical bottles. The physical inventory features of the scanner are powerful, finding incorrectly-filed bottles, identifying disposed/lost bottles, and so forth. It works like a charm.
This is precisely what my library system is looking into. The reason we don’t have it yet? Money. Public libraries are non-profit, after all. Luckily one of our libraries received a large grant to begin implementing RFID, but it’ll be a long time before it’s system-wide.
I can tell you many school libraries DO put the barcodes on the spine, and do inventor the way minor7flat5 describes.
One way is with a portable barcode reader. Later on the inventory is uploaded to a the main computer which will flag books that are out of order. I don’t remeber if the poratable readers were smart enough to flag out of order books or not.
Brian
Used to work for a library software company
I am a shelf checker at the school library. I go once a week and check all the books in my assigned section.
As a patron, I pull books that are misplaced and set them aside for the librarians.
Is that you, babe? 
In college when I worked at the library, we had to check a row of shelves once a week to look for out of order books.
Glad to hear that some libraries are able to do this.
Our chemical inventory scanners are the batch-mode ones you describe (fill-'em-up and dump-'em to the computer back at your desk).
If I were designing our system from scratch today, I would choose RF terminals – scanners that maintain a hot connection to the back-end database application via radio signals. Those would be a perfect fit for library inventory tasks.
They would be perfect - before I started library school in the fall of 2002, I was an internal auditor for a clothing manufacturer. I can remember thinking how cool it would be to take the scanners that that company used in distribution centers and put them to use in libraries to maintain inventory - even to the point of making sure every book that an employee reshelves is scanned - so that you know exactly what’s being used in-house along with what’s being checked out.
The big problem? They can be expensive systems, especially for a small library.