The only ‘upset’ would be Arizona, but they are individually very talented and their guards are very quick. Their first round win wasn't really an upset and playing a 13th seed in the second round made their trip to the Sweet 16 much easier. As for the Final Four, I think Louisville is the safest bet. The only teams that don't have a chance are Purdue, Arizona, and Duke. Purdue is not quick or deep enough; Duke is not a deep team and will get hammered inside; and Arizona isn't mentally or physically tough enough, although their guards are the quickest of the teams left.
One might be tempted to pick Gonzaga, but they have too many mental lapses at the end of games.
I’m not so sure about Louisville after seeing how Siena played them. I think they could be vulnerable.
No one blew out their opponents like UConn did in the first two rounds. And that was with Thabeet looking like he got tranquilized in that Texas A&M game.