I now have an answer (kind of…sort of) to one of the questions I posed back in April when talking about Second Life.
The Pew Internet and American Life Project has released a study on home broadband adoption in the US. Pew reports that 47% of US adults have broadband at home. We still don't know if these are fat tubes or skinny tubes running into houses around the country. That would be interesting data that may exist. I haven't really looked for it.
There are certain demographic categories for households with broadband and it shouldn't come as a surprise. "In particular, broadband penetration remains high among Americans ages 18-49, those with annual household incomes over $75,000 and college graduates." These people tend to also live in urban (52%) or suburban (49%) areas. (p.4)
Hat tip to Stephen Abram.