There's a huge problem with a Bloomberg 2008 campaign, especially a late campaign:
Most people outside the financial industry and downstate New York don't know him from Adam. The lack of any public service experience beyond being mayor of a very large city wouldn't help either. Also, it's regrettable but true, Jews from New York City tend not to poll well in rural districts in the South and West, and such districts have a disproportionate amount of weight given our presidential electoral college system. None of these are insurmountable obstacles, but they all take more than just money and popular stances on issues to fix.
Regardless, probably the biggest obstacle to any presidential aspirations Bloomberg might hold for 2008 is the simple fact that he isn't even running for the office.
"Look, I'm not running for President"
— Michael Bloomberg, December 31, 2007
I don't recommend you hold your breath.