I disagree with you on this one BearCub, just because it's informal (colloquial) doesn't mean that inappropriate use of words is appropriate. Informal would refer to perhaps how you address someone or, as is very common these days, the use of the word "like" 50 times in your sentence but not the word being incorrectly utilized or misspelled.
I'm far from perfect but I agree with Terry that it's annoying to see guys misuse words very regularly. An error is acceptable but consistently incorrect usage is just illiterate. IMHO.
Hmm well i guess we'll have to agree to dissagree on this one. I feel that as long as you're getting your point across effectively, grammar shouldn't really be important. However, i do agree with the "like" issue, because it inhibits your vocalization of your point, and thus does matter because you're not getting your point across effectively.
But as far as their/there/they're, to/too/two, your/you're, etc. etc. etc... As long as people understand what you mean, improper grammar, syntax and/or usage should be non-issues