According to this link (even though it is a little dated), I think the precentage is still pretty high (25% or more). There are also several links that stated the dialup was on the rise again when the economy went south. That kinda makes sense as most people want to be connected but the fastest possible speeds are not always the driving factor. I have several tech friends in large uban areas that still use dial up becuase they refuse to pay ore than there $7 monthly dialup charge. For myself, there is no such thing as too much speed. 100 Mbps broadband just hit my area.... and I though 30 Mbps was pretty snappy.
http://www.internetworldstats.com/am/us.htm
I probably should of added also that even thou 100mbs broadband is available where i live, I can drive 15 miles from my house to more rural areas, and there is no broadband available there.. no dsl, no cable, just good ol POTS. There are some advantages to living in a college town.