The climate seems to be that there's a hunger for an outsider - even more than in 1992. Too many Democrats don't want to create a Clinton Dynasty by electing Hillary, but Obama seems too light-weight (as does Edwards in some respects) and the other major player have too much baggage (e.g. Biden and Dodd), or seem flaky in some respect or other (e.g. Richardson, Kucinich).
On the Republican side, only Ron Paul seems to be willing to say that the mess we're in is, to a very large extent, the result of "conservative" Republican policies. Most of them are running as a continuation of Bush and I don't think the country will buy it again. There are also far too many lightweights (e.g. Romney, and Thompson when he gets in) and religion advocates (e.g. Huckabee) for most people to get excited about their prospects.
That leaves a very big opening for an independent. Bloomberg is a very smart, very rich man who knows how politics works. He's had a significant elected office, and he wouldn't make the mistakes that Perot did in debates and in interactions with the press. He would be a formidable national candidate, but he would have a great deal of difficulty fighting the party establishments for access to ballots and debates and the like.
I don't know if he's going to run or not, but his [link|http://www.nyc.gov/portal/site/nycgov/menuitem.c0935b9a57bb4ef3daf2f1c701c789a0/index.jsp?pageID=mayor_press_release&catID=1194&doc_name=http%3A%2F%2Fwww.nyc.gov%2Fhtml%2Fom%2Fhtml%2F2007a%2Fpr205-07.html&cc=unused1978&rc=1194&ndi=1|statement] certainly makes it sound like he has national ambitions (3rd and 4th paragraphs).