Some kinds of game are going to be a lot easier to make provably fair than others.
Best I can figure, the whole concept of 'provably fair' (as defined here) doesn't really apply to online poker. The closest approximation I can think of might be 'provably fair shuffling', but even that seems problematic because now you have multiple players per shuffle. Just thinking about it now, wouldn't that require every player to know the client seed of every other player? Or maybe there is a simpler solution? I would definitely add this feature to my site (boot52.nl) if I could come up with a reasonable implementation.
But besides all that, there are much simpler ways for a crooked site operator to cheat. For example, the software might have a 'god mode' which would enable certain people to see all your hole cards. You see? So to me, it all boils down to trust. Either you trust the site operator or you don't. And if you don't, then advanced cryptography probably isn't going to help -- at least in poker. At least that's my current thinking. Maybe you disagree? -boot
The issue with online poker is the same as table top poker.
Online == server admin simply looks @ what cards you are holding.
Table == Cameras, bystanders sending signals.
Both == Collusion.
As another user mentioned, you can definitely prove the deck was shuffled randomly but you cannot prove or disprove admin honesty in this situation. This is why I only play with small change, Im after a cheap thrill and due to my cheapness Im not an ideal target for a scammer. Its why this is such a classic scene in movies:
Pub + poker table = flip table + gun shoot out.