I try to stick to plain old mpeg1, but also use wmv when its embedded in a tour just to cut down on the size of the download by everyone and their dog. Its funny I got an email just this week from a member thanking me for using mpeg1 cuz he knew for sure that it was compatable with his mac.

I am not saying that embracing new technology is a bad idea, but just be prepared to do a lot more support and deal with more refunds/chargebacks on paysite accounts.

cheers,
Luke