I would be shocked if he ran. He has a pretty safe House seat and I think he realizes that 2010 is probably not a good year to try for a very uphill battle at a Senate seat. Look at Mary Landrieu's narrow 52%-46% win over a weak Democrat-turned Republican with the swelled black turnout that wont be there in 2010.
But wouldn't that be more than cancelled out by the lack of McCain's coattails? That surely helped make the the Landrieu/Kennedy senate race as surprisingly close as it was.
Regardless, I agree with the general concensus that the most likely outcome of Melancon running would be a GOP pickup in the House.
If Melancon were to run and the GOP picked up that House seat and assuming that Joseph Cao gets reelected (which I don't think he will), that would give the GOP every Congressional seat in Louisiana, wouldn't it?