I was pointed to John Foley's InformationWeek article earlier this week of "20 Cloud Computing Startups You Should Know." Aside from the fact I could only count 19, it was a great survey of what types of companies, ideas and ventures are getting on the bandwagon.
The quick-and-dirty chart above is mine; what I found so interesting is that 8 of the players are building solutions on top of other clouds (like Amazon's EC2 and S3) while another 7 are investing in essentially building hosted services.
However, only 4 (ok, maybe 4-1/2) are thinking/trying to bring "cloud" technologies and economics to the enterprise's own internal IT. This certainly attests to the difficulty in reworking IT's entrenched technologies, and building a newer abstracted model of how IT should operate.
Even though Cassatt wasn't mentioned in the survey (maybe we were supposed to be #20) we also play in the "build-an-internal-cloud-with-what-you-have" space.
This model -- that of an "internal cloud" architecture -- will ultimately result in more efficient data centers (these architectures are highly efficient) and ones that will be able to "reach out" for additional resources (if-and-when needed) in an easier manner than today's IT.
I'd look to see more existing enterprises considering building their own cloud architectures (after all, they've already invested lots of $$ in infrastructure) while startups and smaller shops opt for the products that leverage existing (external) cloud resources.
BTW, John also just posted a very nice blog of a "reality check" to curb some of the cloud computing hype.