Larry Ellison has stated that Cloud Computing is "everything that we already do", and In many ways, I totally agree. The big difference is that Cloud-based technologies let us do everything much faster, smarter, and often at a greatly reduced cost.
Cloud Computing encompasses a lot of areas (and we go into more detail below), but whether you're talking about Google Apps or AWS, "the Cloud" brings some very disruptive changes. Here's the broad strokes:
Everyone who knows Rackspace usually has two comments about them -- "Fantastic support" (they brand it "Fanatic Support") and "Expensive". With their Cloud Servers offering, they're putting the final nails in the coffin of the "Expensive" comment.
We've been hosting multiple domains (including this site) on their Rackspace Cloud (RSC) Servers for several months, and I could not be more pleased. You still get the "Fanatical Support", unlimited 24x7 Chat & Phone support, and you pay a whole lot less... for a better product.