I think its rude to point them out; I type very quickly, and sometimes I make typos, and post before iv'e really looked it over. Most of the time I know people know what I meant to say, but if its really funny, I'll make fun of myself.
That being said, I do have a couple of friends who I will jokingly tell, hey, that's wrong, and they will do the same to me, but we are not serious, and just do it to give each other a hard time, thats the nature of our relationships. ONe friend posted something the other day and meant to say 'won" but typed "wong" - so of course I had to jump right on it, in fun, but she gave it right back to me! But most people I won't say a word.