There are a couple of other noteworthy points regarding contacting ebay members. They provide alternatives to contact buyers from directly reading the IDs from completed auctions, but do require a little creativity & extra work.
1. Aside from the blind PM to a user, you can ask any user with a listing a question. Granted you have to bypass ebay's attempt to automatically answer the question and send you on your way, but as long as you insist on asking the seller, you can send them a message. Once you get to that form, you can ask them about anything & include your e-mail address for an offline response.
2. Although the scrambling IDs prevents direct knowlegde of a winner's ebay user ID, as many of the forum detectives already know from trying to track down rare items like the fang glass, you can watch a seller's feedback, and that will show the buyer's ID for the auction provided the feedback isn't private and the seller leaves feedback.
3. Additionally, the scrambling is not random. Once your ID is scrambled, it's the same in all auctions. Once you confirm a bunch of heavy hitting bidders, you can usually tell who the bidder is even if it's scrambled. I know any sketch auction that has a f**9(x) bidder is Leslie. To confirm, you just have to match the feedback number in the bidder's list to their actual feedback once you look up their ID.