That doesn't bother me all that much but ridiculous grammar and spelling is comical. 
It seems very few people know the difference between similar words:
to vs too vs two
lose vs loose (my all time favorite)
there vs their vs they're
...and on and on
		
		
	 
I feel you, MDS.  Some posters elsewhere even have these distinctions as their "sig", lol.  
Sometimes I think the mistakes come from laziness.  Then other times I do believe they are completely unaware of the distinctions.
In defense of a few* mistakes that occur, I do find myself typing very quickly at times, and do end up typing the wrong word simply due to muscle memory, believe it or not.  For instance, for a while there, EVERYTIME I wanted to type/say "possible", I kept typing "possibly".
Another one that people should be aware of, at an audio forum of all places, is the distinction between "base" and "bass".
** you're not going to believe this:  Just previewed my post, and I typed "possibly" TWICE.  See, I'm not lying!  
 
EDIT: I think another contributing factor towards poor grammar might be the increasing number of folks who are posting with something like a crackberry or iphone.