I don't like IFL's chances to blow the UFC out of the water when they have "Superfights" like Wes Sims vs Daniel Gracie. I like the IFL though and it has alot of potential. It will be interesting to see the rosters of the new teams that have formed. They still have a long way to go till they are on UFC's level though IMO.
As of right now the only serious threat I see to UFC as far as US organizations go is WFA. The new WFA has really put together an excellent card for their rebirth. I don't know if they will be able to continue to do this time after time, but it's a great start. Strikeforce has alot of potential too, but they have yet to be on PPV or TV, so I don't think they are a serious threat yet.