I always figured it was a massive, rude spoiler, like this T-shirt.
Wow, I might have throttled someone wearing that t-shirt. 
The hand papermaking information is rather lacking. I whipped up some stuff about rice paper, but it’s not very good.
Absolutely, especially concerning pre-modern Japanese history and politics.
Wikipedia’s coverage of manga is also quite poor, especially considering the breadth of information included about the most insignificant anime. And if a manga has been turned into an anime, it’s wiki entry will be a lengthy description of the anime with the manga mentioned only in passing.
There used to be an article on deceased wrestler Happy Humphrey, one of the heaviest pro wrestlers of all time. The article was not particularly well written, and not well sourced, so someone deleted it. It’s really hard to find reliable information on deceased old-school pro rasslers.
Perhaps I will if I find the time. The main barrier is that I don’t have the reference materials at hand. I’m familiar with the subject in a general way, but I don’t have the details memorized. I have a cordial dislike for articles on historical subjects that amount to not much more than anecdote or the result of a game of telephone.
Last week I decided to use wiki to help me put my MP3s in their “correct” genres. About 25% of the bands I’ve looked up have no entries 
You might like to try the gracenote database? I believe that’s what iTunes looks up when importing a new CD.
Hmmm…now that I look at it, I don’t think it tells you genres for CDs…
Without reading the thread (sorry! :o ), I will note that, at any time, you can go to Wikipedia’s Community Portal, and there you will find, among other things, a list of “Requests” for articles that people have made. It’s always quite long, filled usually with people and places, and interesting to read. If you really like to be a good do-be, you can always pitch in and help. It’s infectious. 
I was looking for an article on U.S.-Vietnam relations yesterday and couldn’t find one. Yesterday was the 12th anniversary of when the two countries normalized relations and I was surprised I didn’t see any entries on the history there.
OK, here’s my pseudo-wiki: during the 1960s we had a convergence of the first wave of LOTR popularity in the US (coinciding with the paperback release), and the “protest button” – pithy saying pinned to one’s clothing, often with a counter-culture or anti-war phrase. A popular button of the time was one saying “Frodo Lives”, which would be completely obscure to those who hadn’t yet read the books.
Ignoring for the moment that Frodo’s a fictional character in a fantasy world, he is technically alive at the end of LOTR, and sailing to the Undying Lands. But those few mortals allowed to reach the Undying Lands are not granted immortality, just surcease from sorrow for their remaining allotted lifespan. So “Frodo Lives” only metaphorically, in the same sense that “Che Lives”.
My graphic novel series. Anyone feel like typing? 
In my experience, Wikipedia is very useful for U.S. popular culture, U.S. history, computer science and mathematics. I’m sure there are other areas in which it excels. However, one place in which it is very easy to find deficiencies is to look up minor characters or events in the history of a foreign country.
There is no article on Costa Rican beers, just a sentence or two on the Costa Rica Cuisine page.
That’s what I did a few years ago when I found that Wikipedia didn’t have an article on the Free Surface Effect. I wrote a quick little piece (A couple of simple paragraphs), and it’s gone through several iterations since then, that I’m aware of.
Anyways, to answer the OP: Yes, I’ve been frustrated by a lack of entries on a specific topic in the past. Not often, but it’s happened.
There are some great American bridge players who have no biographical info in wiki.