Slicehost: Boot your slices with your own custom kernel
slicehost.com
slicehost.com
I can't think of any other new features SliceHost has rolled out in the last 6 months.
(I'm a Debian guy) I used 'dpkg -l' to check what all I had currently installed and narrowed down what packages I was still using. Check /etc/init.d for start up scripts. Hard files on disk are easy to migrate, live migrating MySQL data is more tricky, but my personal sites don't really have that much going on. I always keep a .tar.gz of the entire server for future reference.
Move over as much as possible and try to get things running. Save your .bash_history and get a build script going. Pull any /etc/ config files you are missing. Reinstall your required packages. Test your new site via editing /etc/hosts, then move the DNS. Watch your logs and look for 404 erors for files you didn't copy over correctly.
It takes time, but if you use an organized and repeatable process, it can take less time in the future.
It goes through the trouble of installing all of my various dpkg dependencies, setting up mysql, downloading and compiling rails and nginx w/ passenger, as well as setting up my bash prompt.
This update make me wonder if Rackspace is seeing that there was more to slicehost then just the platform, and maybe considering focusing on the slicehost brand.
I still love the Slicehost docs and use them even though I'm on linode. If it looked liek Slicehost wasn't being ignored I would gladly move back.