In her post, Paddy asks who would vote for Bloomberg? I think there are a lot of people who would do so. I mean, Ross Perot got a decent share of the vote in 1992, and he was friggin nuts. Bloomberg is a much better politician than Perot and he also has political experience. With his campaign funding (he could self-finance to the tune of at least $100 million), I think he could easily get 25% of the vote.
The danger of a Bloomberg candidacy is that it could allow a very conservative GOPer, like say, Fred Thompson, to sneak in the White House. The Democrat would get core Dems and some independents, Bloomberg would take mostly independents, and the GOP candidate would get core Republicans, winning the South and Midwest. It's possible that an independent candidate would do more damage to Democrats at this point than Republicans, but that remains to be seen.
The most interesting aspect of a Bloomberg candidacy, however, is what if he runs, Giuliani wins the GOP nomination and Hillary Clinton wins the Democratic nomination. That would mean the country would have to pick between two mayor's of New York and a New York Senator. What would the South do?