Actually, I made the switch from Slicehost to Rackspace because it was cheaper. It's pay for what you eat pricing, so you don't get a free allotment of bandwidth, but it's around ~$11 for a 256 meg instance.

My biggest concern is that the Rackspace Cloud product doesn't seem as polished as Slicehost. Slicehost was a great service for newer users, with great documentation and help resources.