To be honest, I understand very little about what makes any of today's web-based startups "hot", but today I ran across two lists.
The first is "The 20 Hot Silicon Valley Startups You Need To Watch".
The second is "The 20 Most Innovative Startups In Tech".
What makes them the "hottest" or the "most innovative"? Hard to say. My hunch is that it is simply their investors touting them.
My concern is that we may be back into the "flip it" mode of investment where there is little concern about long-term viability and long-term profit generation, but simply whether the initial investors can flip the startup off to some unsuspecting bigger fish in the pond. A lot of these ventures really do seem to fit the bill for the old Silicon Valley adage of "That's a feature, not a product." except that most of them are web-based services rather than "in a box" products anyway. OTOH, maybe being a "feature" is a better (or at least easier) path to success than a full-blown "product." On that angle, here's an interesting commentary about Dropbox turning down an offer from Apple.
-- Jack Krupansky