Bloomberg's reelection as NYC mayor has got to give him pause. He ended up spending something like $30 million dollars to beat a nobody by less than five points.
Also, there's a question of what he'd run as. Bloomberg was a Democrat until the early 1990's. If people don't recall that, they'll quickly be reminded.
The RINO tag will be hard to avoid. As well as the <I bought the election> tag. Bloomberg is probably rich enough to float his own presidential campaign. That's something to consider.
There's no way the Dems would take him back anytime before 2016 and if they did, the electorate would reject him.
DEM -> GOP -> DEM? No way.
Bloomberg would almost have to run as a third party candidate, and to do so successfully he needs to ride the high-tide of anti-system voting. When the people who don't usually vote in the US (about half) start to get activated, the results could be interesting.
OTOH, Bloomberg is 68 years old. But the high tide of anti-system voting might not be in 2012. It could be in 2016 or thereafter, but by then, Bloomberg will be (at least) 74 years old.
Has Bloomberg been making noises, Manny? Would the GOP really take Bloomberg?
That seems unthinkable to me.