That’s got to be one of the most frequent recurring questions here, with “YMMV” near the top as well. I know that buried deep in one of the FAQs is a link to what all these shorthands mean, but, well, it’s buried. Along with the usual netspeak, we can probably add in SDMB-specific abbreviations, such as “SDSAB.” This can be done either as a link to one of the many sites that explain netspeak or in the form of a thread where Dopers add in their own contributions.
Along the same lines, perhaps a sticky of the “greatest hits” would probably be a good idea as well. Once in a while I’d notice surges of “Does a duck’s quack echo?” “Does 0.999~ = 1?” and a handful of other topics, and it’ll probably save everyone a lot of effort if these questions can be directed to a sticky.