Incorrect spelling, punctuation, and using incorrect words irk the crap out of me too, but I ignore it on a public forum. I cringe in the privacy of my own home. The only time I would point it out is if I were teasing someone, or if the post was by someone on their high horse, calling someone else ignorant, and being nasty. Then I would most happily point out their own ignorance.
However, one thing that has been happening with a great deal of frequency lately is the number of books that are released with such errors. I think that if you publish, you should have a proofreader. And don't get me started on newspapers!
I also agree that all caps, really large letters, multiple fonts and colors can be a bit jarring, and really makes the post more difficult to read. But I am guilty of using all caps sometimes when I am at work, because my main program uses all caps, and I am too lazy to continually switch all day.
As for me, I am decent with spelling and grammar, but my fingers are incredibly clumsy creatures, and hit the wrong keys all the time.