I don't have a convenient way of segregating my paid and non-paid Bing traffic, but I thought it might be interesting to try comparing to paid and non-paid Google traffic for giggles. The conversion of interest for me is a trial download. I'm analyzing the data only from the date Bing was publicly released.

Google (free): 10.4k visits, 12.76% conversion

Google (paid): 5.2k visits, 21.61% conversion

Yahoo (free): 1.2k visits, 18.64% conversion

Bing (both): 945 visits, 17.69% conversion

I'm not exactly seeing the sort of results that it would take to make me mentally retool my SEO thought processes away from "give Google what it wants". For instance, that volume problem you're talking about is an absolute killer for me -- there is no way I can justify rewriting my ad text to match the habits of Bing searchers when at best I'm going to be getting a couple hundred clicks a month on ads.

(The lower conversion on Google searches is because, in the course of giving Google what it wants, I have ended up ranking for a high-volume term or three whose searchers are not looking for what I have to offer. The biggest offender is [bingo cards].)