As a native New Yorker I have a great deal of respect for Mike Bloomberg. Though I haven't lived in New York since I left to go to New Hampshire for Bill Cinton in 1992, my friends there all say the city has improved a great deal and credit the Mayor. So let's give him that. The problem for his nascent run at the Presidency is that is simply the wrong year for him and what he thinks he might be able to do for the country. I offer to two primary reasons:
1) The math of a 3rd party candidacy is very tough. Even if he can get on the ballots of all 50 states, the electoral math is almost insurmountable. Consider that to get to a plurality, 34%, he would have to keep both major parties to a total of just 66%, or 33% each. Doing this would require both two major parties to get a lower vote than they have ever gotten since the GOP was founded in the 1850s (I'm sure there are scenerios that his team has crafted that show him winning without a plurality but they all seem far-fetched).
This kind of scenerio would require the functional collapse of both major political parties for him to win. Is that possible in 2008? It's possible, as national polls show one of the two parties, the GOP, consistently in the low to mid 30s. The problem for the Bloomberg scenerio is that a collapse of the Democratic Party seems implausible as the Democrats are in a stronger position today than they have been in at least a generation.
Let's review the numbers. In 2006 Democrats received a higher national vote total - 53% - than they had received since at least 1982, and was one of its highest national vote totals in the last 100 years of politics. Party ID and the Presidential/Congressional generic polls show consistently very high numbers, in the mid to high 40s. Democrats are raising more money across the board than any time in its history. They are using new and powerful tools that allow them to reach and engage many more people very effectively. Their agenda is in synch with the country right now. They have a good Presidential field, and are will likely produce a nominee who can keep the party itself together and prevent a slippage from its mid 40 standing right now. All in all in the Democratic brand is very strong right now by any historic measure.
So what Bloomberg is looking at is a race where the Democrats start in the mid 40s, and appear likely to stay there, and the GOP is at 33 or so. This leaves Bloomberg with an available pool of about 20 percent of the electorate. Winning would require him to win all those voters and somehow knock the Democrats down 10 points nationally, into the mid 30s. All of this seems very unlikely, even if he was a charismatic candidate capable of exciting millons of people.
2) His connection to Bush. I don't really know how Bloomberg can overcome his GOP affiliation. He has raised millions of dollars for GOP candidates, and was instrumental in putting on the 2004 Convention that re-elected Bush. There is a strong argument to be made that he did more to re-elect Bush than anyone else in American in 2004. The simple truth of this is something that be exploited easily with paid media, and significantly undermine his "independent" positioning in an election that will be one longer intense repudiation of the Bush era.
Much more will be written about his potential candidacy, but I think the idea of a Bloomberg presidency is a fantasy. If he runs he will likely do what Perot did in 1992 and weaken the GOP, help elect the Democrats (1992 ended 43 Clinton, 38 Bush, 19 Perot) and take himself out of contention for being a potential interesting VP candidate for the Democrats.