Isle of Mann is pretty solid. Kahnawake is from what I understand little more than a criminal enterprise.
I can in general vouch for the legitimacy of pokerstars, seeing I personally know many of the people that run it... although now they are out of the country for the time being and I don't see them anymore.
The thing that a lot of people don't grasp is that online poker presents an unprecidented opportunity to statistically analyze poker hands. The UB/Absolute scandal was unearthed by players who had saved millions of hand histories and noticed that a player was winning at what was a statistically impossible level. They then more closely analyzed the play and saw the player was acting as if he could see the cards of the opponent, and went from there.
The sites, at least the legitimate and established ones use programs that analyze hands with full knowledge (after the fact) of hole cards that send up red flags when the data suggests a pattern that indicates collusion. You trade some (in part illusory) security because of no direct observation, but you gain much more by being able to track data.
Similar things could be said about internet sports wagering. The lack of legitimate betting houses in the US makes it far easier to fix games and get away with it. If you have legal internet wagering, most people are going to use it and illegal bookies will lose quite a bit of market share. It thus becomes harder to place bets that can't be tracked.
Anyway, a lot of the debate on the house floor about this bill centered around the fact that it was sucking money out of the US and wasn't helping GDP. Whether that is why it is illegal, it is a part of why it was outlawed.
This of course violates several free trade agreements and as I understand the US has some liability for doing so.
Barney Frank is da man:
His speech in part: