Dmitry Sotnikov is trying to answer this question at his enterprise cloud blog. He doesn’t try to be comprehensive. It’s a lot easier to look at the sales of large public companies since they have to provide so much disclosure when they make capital investments. And of course, the big vendors have been sinking large sums into their cloud infrastructure so they have needed to justify that with some public statements about the returns they expect from all those servers and data pipes they’re configuring.
Dmitry considers only Saleforce, Rackspace, Microsoft, Amazon, Google and IBM. At least IBM is easy because there is a statement from CFO Mark Loughridge projecting $7 billion in cloud revenue by 2015.
On the other companies, it’s not so clearcut and Dmitry works the numbers pretty well at his post How Much Money Do Cloud Providers Make?. Worth reading if you are looking at the financial opportunities in cloud services.