Is it just me, or is it nearly impossible to know when to use who/whom? Of course, if you KNOW, than you're laughing right now. Actually, I've known for a few months, and how did I find out? An english teacher? No - I asked, trust me, and was always confused. A grammar guide? No - Elements of Style failed me just as miserably. Then how? Well, my friends, I'll tell you.
Ah! Such marvel, such mystery, such magnificence! And how did the internet teach me what teachers had failed to do for 12 years? By making it simple.
Who is correct in instances when you would say 'he' or 'she.'
Whom is correct in instances when you would say 'him' or 'her.'
As is... "he is here?" "Who is here?" and "This belongs to him?" "This belongs to whom?"
Now, I'm not sure this is always correct, but it seems to work pretty well. Far better than my previous policy of going with, you know, whatever sounded good.