We recently fielded a query from a client who has a long running, general population telephone survey but now faces some internal pressures to consider mail. His request to us was to supply him with some information to help with that decision. Dan Zahs and I put our heads together and produced a short overview of the issues. You can see that document here.
Over about the last 20 years telephone has generally been preferred over mail for general population surveys with mail's most attractive feature being its lower cost. Of course, with deterioration of the RDD sample frame and continuing concerns about Web that could change. Mail surveys could become more attractive, although the frame available to do really good, representative mail surveys is still being evaluated. It's all in the overview.
But as of this writing this geek still likes telephone.