Obviously, AOL and EarthLink are seeing a decline in numbers (each lost about 1M, according to DSLReports) as dial-up users shrink. DSL is slowing according to PEW. This might be due to the fact that much of the dial-up base that wants broadband has converted. However, "Technically, the nineteen largest cable and telephone providers in the U.S. account for 94% of the [broadband] market," according to DSL Reports and ISP-Planet.
"47% of all adult Americans now have a high-speed internet connection at home, according to a February 2007 survey conducted by the Pew Internet & American Life Project." [source]
"Rural Americans: 31% of those living in rural areas have broadband at home, up 6 percentage points from 2006. "
The problem becomes how do you get more internet enabled devices (i.e., PC's, laptops, mini-computers, media center servers) into households without devices? Also, how do you market to the older Americans, women and Hispanics - the segments that are growing the fastest?