Who shot whom in the what, now?
Cite? It’s not just preferred to not separate a preposition from its object, it is correct. I will concede that it is acceptible in informal settings, but it is still grammatically incorrect. And even though it may be socially acceptable, English does not have separate formal and informal grammatical structures, such as German, for example.
I’ll be the first to admit that I say that very sentance, “who did you arrive with?” even though I know it contains two errors. Saying it correctly just isn’t part of our vernacular.
P.S. There is no “l” in my name. 
Nah, English relies on word order heavily enough that we don’t really need cases. Similarly, we could get rid of “I” and just say “me” everywhere. Nothing ambiguous about “Me has of late, but wherefore me knows not, lost all me’s mirth.”
Whom you gonna’ call? Ghostbusters!
Could I just step in to the triesome arguments about ending sentences with prepositions and try to answer SeekingTruth’s original question as simply as I can.
I always had trouble with this until someone told me how to figure it out. Rewrite the sentence using either “he” or “him” in place of “who”. (If it’s a question, write an answer to it in the same format.) If “he” makes sense, then use “who”; if “him” makes sense, then use “who”. This does not need complex parsing of the sentence structure, which can get tricky.
Examples:
“Who/Whom shall I say is calling?” = “I shall say he is calling” (“him” would not make sense here). So use who.
“I live with Bob, who/whom I must confess I detest.” = “I live with Bob; I must say I detest him”. So use whom.
“Who/Whom does he think he is to tell me which word to use?” = “He thinks he is an expert on English”. So use who.
Get the idea?
I assume this was a joke, but just to illustrate again why it is correct, strictly speaking:
“Whom [are] you gonna call?” = “I am gonna call him”.
You beat me to it.
Hmm, on re-reading Polycarp’s post a bit more clearly, he beat me to it as well with the all-purpose ultra-simple explanation.
It is kinda’ funny, but thats honestly the example i’ve always used to keep it straight in my head 
Polycarp, Mr2001 and r_k:
THANK YOU!
If you are willing to take a cut in pay, become English teachers.
I GET IT NOW!
dance
I think you’re saying that it’s incorrect to end a sentence with a preposition whose object began the sentence. But that’s wrong - it is correct (if informal) English. It’s also correct to use “whom” for its object. Here’s a cite. Above, robcaro posted the usage note from the AHD:
I got tired of reading the posts so the answer might already be on here. If you’re not sure, just exchange “him” for “whom” and “he” for “who”. If the sentence still sounds okay, then you’re using the correct word.
Example: To whom does that belong? = Does that belong to him?
Who eats cheese? = He eats cheese.
I’ve seen this rule of thumb in many places including a pocketsized English book, an old Reader’s Digest and some website. I’m too lazy to cite, but trust me, I know I’m right.
G.
Gllrnz, I said earlier I got the point (same as your explanation). Some threads never die.
MODS! DELETE THIS POST< PLEASE!
Shit, I meant thread
Whom' is dying, just as the familiar and polite forms of you’ died in Shakespeare’s time. Quick: How do you address someone who is of a higher social rank than you are? If you answered ye', that's correct. Or rather, was correct. [Now, it's simply you’.](http://home.bluemarble.net/~langmin/youpol.htm) We lost the distinction about the time Britain gained its first New World colonies and printing presses became relatively common and began to exert a standardizing influence on language.
Learn how to use it, but remember: Pedants die, and when they do it falls to linguistic historians to preserve the words and distinctions. And linguistic historians aren’t interested in making people speak `correctly’.
OK, on a related note… (ie vague hijack)
I have no problem with the difference between “who” and “whom”. Several years of studying german helped me learn the intricacies of that situation.
My problem is “which” and “that”.
Can someone please explain when one should use “which” and when one should use “that”?
For example:
This is the lawnmower that I need to take in for repairs.
This is the lawnmower, which needs to be repaired.
Which of those sentences is correct, if either?
How does one know how to correctly phrase when using “which” or “that”?
In your examples, “that I need to take in for repairs” is a restrictive clause in that it limits the scope of the noun “lawnmower” to only those lawnmowers that you need to take in. Your “which needs to be repaired” is a non-restrictive clause– it merely provides additional information, which might apply to other lawnmowers.
The general rule is that a non-restrictive clause should always start with which and should be separated from the rest of the sentence by commas. Restrictive clauses usually start with that although it not necessarily wrong to use which, and you should not use commas. So both of your sentences are correct, but they mean slightly different things.
Oh for god’s hairy butted sake, you don’t have to be so rude. I said I didn’t read them all, and besides what are you doing reading them anyhow if you already know the answer? Do you talk to people like this in real life? If so, I’m glad I don’t know you personally.
G.