I rarely use abbreviations in my typing, nor do I use a word-check or grammar check very often. I will if I'm writing a paper that I have to turn in, just in case, but I rarely listen to the grammar check on Word, since it makes worse mistakes than I do, and half the time, the spell check doesn't have the word I'm trying to spell anyway. Stupid microsoft word.
I don't type poorly or use abbreviations not because I don't want to fall into a "bad habit", but because I want to type the way I should.
I type very fast, and I learned how to type properly. I worked as a typist for a newspaper and as a secretary, and then when I got into school, I had a lot of typing to do for papers, and my own hobby is writing short stories (with the intention of one day writing a real novel...). So, I started out by typing properly and I continued to type properly to the point that I have to make a determined effort to type improperly. So, for other people, they have to make an effort to type properly, and they don't if they don't have to. I have to make an effort to type improperly, so I don't if I don't have to. :)
My grammar likely isn't one hundred percent perfect. But it is readable. I don't use ; and :'s properly, and I'm told I overuse the , ... , but I'd rather overuse than underuse, so long as I don't go overboard, and, start, doing, something, like, this (which I can see a certain someone on this thread doing, just to prove a point :).
I learned to type properly, and while I don't look down on others who use abbreviations, "ur", "l8r", etc, I also won't use them. Why? Call me a snob if you will, but I also don't use "ain't", "my moms" and other incorrect ways of speaking. I wasn't brought up that way. So, I never used it, and I don't use it, and I won't ever use it (unless I'm writing dialogue for a character or something like that). Does that make people who use things like that stupid? No. My brother can't spell or type properly and he's pretty smart. My mother has atrocious spelling and she's pretty smart. I went to college with someone who used "my moms" consistently and it drove me nuts, but she was very smart.
The only times I ever abbreviate things is when I'm on a board or game where there's a limit to how much you can type in a single message (like FFXI, where you have two lines), and if I'm in a rush, I'll use common abbreviations like lvl and ppl. I still don't use ur and l8r, though. I do use LOL, BRB, AFK, etc, because those aren't contracted words, they're acronyms for something. (Yes, I know acronyms are usually things like L.A.S.E.R and R.A.D.A.R. and B.R.B doesn't count because you can't pronounce BRB in a sentence (well, you could try...) but I don't remember what the real term for BRB and AFK and the like are.)
And.. I am QUEEN OF THE RUN ON SENTENCE! However, my sentences are punctuated properly and I like paragraphs. Paragraphs are my friend.
Sorry. I like ,'s, parenthesized comments, and paragraphs. :) I tend to wax eloquent about them, when I have to talk about grammar at all. ;)