Even though I am not studying the module as part of my Masters I had to buy due to my intense interest in the subject area.
It is essential reading for anyone doing the sociolinguistics module on the MA Applied Linguistics/Linguistics. It is a very informative read for anyone doing any other module in the field of Linguistics/MEd etc. One is able to encorporate the learning in this book with other reading and apply at a practical level whether at work or undergoing academic research.
Gives a treetment on Variationist/Gender/Age etc. as well as research in the field.
I am a bit biased as love the topic area but it is required reading in some university courses anyway - so there.