Downloaded the PDFs. I wouldn't ever use them for actually running a game, but they did confirm that I like the direction of 4e and make me want the actual books (I hate reading PDFs, even if they are good quality non-scanned versions). Had the "cup of coffee" priced versions been out at this point, I would have bought them instead, and probably will buy them when they're available (or if they aren't for some time, I'll merely buy the books and attach my receipts as one poster mentioned). I mainly wanted to peek at the "example of play" and the art. Given that I don't actually have a group anymore though, me buying or not probably matters little. Even though I will be buying them in a week (or whatever) simply to read through them and look at the art.
Given this poll is at ~260 posters and only 4.5% said they wouldn't buy the books because of the PDF (whether it be because the PDF made them decide not to or the PDFs are enough for them to play with) it seems like this might be a representative sample, and thus seems like little negative impact. I doubt seriously that PDFs (even in 3.5e) had a serious effect on sales, given the general unpleasantness of using PDFs for games books. Likely the most affected books were those that already had little appeal aside from some specific rule or mechanic.