Bigtime, The lists are worth a lot of money because sending out mailers to people who won't act on them is expensive.

I'm simultaneously creeped out and impressed by the Comcast commercials that offer to target ads by age, sex, voter status, and other demos. They cross compiled all sorts of databases to get that info.

I came across this a couple hours ago while reading Solove's book The Digital Person. There are several pages devoted to all of the different lists you can buy. Apparently there are over 550 companies in this business (as of 2004).