I have never had the privilege to sign up with their cloud sites that start at $100 / month, it's a little too steep for me. However, backed by Rackspace, the cloud servers is simply the best hosting package on the web: responsive, nearly-zero downtime and affordable.
Their control panel is amazingly simple yet powerful enough to get necessary things done. I especially like the way the backup system works, doesn't charge any fee right now but heard they were going to.
It's absolutely a pleasure to be on their cloud vps, I learned a lot there and if you had any trouble running your own slice, just head over to their documentation or you can read my article to set up a naked ubuntu distro for LAMP.
P.S. Appears their cloud servers are hosted on Slicehost.