I've not been with the internet since it began, by any measure - I'm pretty sure we never had a modem slow enough to be measured in "bauds", for instance. I have been participating online for the majority of my conscious life though, mostly on forums but occasionally IRC channels too (not hacker ones; I've never had much of an interest in the misuse of computers).
I don't remember there being quite so much slang thrown around as easily or as widely as it is now, though. There was always a "lol" here and there (I made a conscious decision to stop using that particular acronym not long after I first encountered it), maybe a rofl or lmao, but there's a bewildering number of shorthand phrases around nowadays.
Okay, that paragraph made me sound (and feel) ridiculously old.
I'm a bit of a sticker for grammar, but for some reason the acronym shorthand common online isn't half as annoying as txt spk abbreviation or l337 5p34k letter substitution. I suppose it's because an acronym preserves the meaning and order of words, and although they've been cut down to a single letter each I don't have as hard a time deciphering it1.
There's usually enough context in the words or familiar acronyms around jfc for me to figure out wtf it means, but it feels like a barrier designed to keep my fogey brain out of these youngsters' internet. Or maybe I'm just getting paranoid.
1 The trick, I've found, is to work out one of the words from the context and work from there. Also, and "f" is usually pretty obviously profane.