I submit the following two sentences. Similar in appearance, but very different in meaning:
"I'd like to thank my parents, Ayn Rand, and God."
"I'd like to thank my parents, Ayn Rand and God."
Please don't omit the last comma from a set. It's an awful convention that was started to save space in newspapers (because technically, each additional character costs them money). It has no purpose here, and can never be better than leaving them all in.
(Conversely, do not insert an extra comma where none should be, or in some random place, e.g. "You are an illiterate, offensive, jerk." A decent test is to ask yourself whether you would pause if reading the sentence aloud.)
"Internet" and "Web" are proper nouns and should be capitalized. Most people don't do this; I didn't for years. But if you want to be picky, there you go. Also, they are not synonyms.
I've always liked these pages:
http://www.ecn.bgu.edu/users/gas52r0/Jay/spelling/looselose.html
http://angryflower.com/aposter.html
If you want some information overload:
http://www.wsu.edu:8080/~brians/errors/errors.html
Finally, being too strict can be detrimental. If you get all hot under the collar when someone starts a sentence with "But", even when it sounds better that way or works well for pacing purposes, that's unreasonable in my mind. Dangling participles aren't the end of the world, except for maybe the really stupid ones ("Where's the library at?"). "Myriad" can (allegedly) be used as either a noun or an adjective now. "ATMs" versus "ATM's" is a national thing, but I prefer the non-US way (no pointless apostrophe). "ATM machine", on the other hand, is redundant. So is "SCUBA gear", but that one's less obvious.
Language is constantly evolving, and the purpose of language is to communicate and/or to artistically express yourself. I'm hoping that English doesn't "evolve" in the direction a lot of Internet users seem to want to take it, but it is a fairly complex language compared to some. That said, I feel that while complexity makes communication more difficult, it leaves more room for artistic expression, so there has to be a trade-off.
Whew, what a windbag. I guess what I'm saying is that as long as someone gets their point across without being too horrible, I usually give them a break. If not, I guess I'd have to be a Beastmaster, because I couldn't stand to talk to anyone (my distaste for "lol" would disqualify most, if not all, of the entire FFXI population).