around here, we tend to be pretty casual about the internet abbreviations. trust me, if something is going to make us mad, that's not the one to worry about.
the dom/sub thing that some people use (here or elsewhere) is that the top or dom is capitalized while the sub or bottom isn't. i think some people on here follow that rule, but a lot don't. either way is fine, it's about which style you personally prefer.
i often type without capital letters, but that's mostly because i can't be bothered with the shift key (just be glad that the part who can't be bothered with punctuation marks doesn't generally post here!).
oh, and here's an abbreviation that's pretty specific to this board: w or i will refer to "ea" which is short for "establishing authority." it used to be "sunday" or "sunday maintenance" (meaning a check-in and spanking that we'd do on a weekly basis), but we don't always do it on sundays and we decided to call it establishing authority instead of maintenance, since that's a better description for us.
but don't worry--we rarely mind explaining what we've meant, and we're unlikely to get upset about someone who doesn't know our quirks.