I picked up an intro to sociolinguistics ("Sociolinguistics" by Peter Trudgill) a while ago, but I decided it was a bit too fluffy for me. It was basically 200 pages of "Everything affects the way we speak", with some examples.
Something that did surprise me, actually, while reading Trudgill's book was my opposition to one of the points he kept coming back to : all dialects are equally good, valid, and worth preserving. This is clearly the logical extension of my position that I dislike prescriptive grammarians and prefer descriptive grammarians. Perhaps there's just some middle line that I just haven't found yet. Or maybe I've become a language snob without noticing? Maybe I should just accept the fact that for the moment I hold two contradictory world views. Oh well.
Anyway, I headed back to the used bookstore and found another sociolinguistics textbook, this one slightly more rigorous. It was actually the second volume of a two-volume set. The first book was "The Sociolinguistics of Society" and was aimed more at the society end of things, while the second book, "The Sociolinguistics of Language", dealt with more of the linguistics end. I haven't really read much of it yet, but from what I have read it has the more academic approach I'm used to and expect from my books.