I have a VPS hosted at RimuHosting.com. I waited a while (3 months) for bugs to be squashed before upgrading it to Ubuntu Linux 7.10 (“Gutsy Gibbon”). There was one new issue.
BTW, my non-Rimu home server was the first thing I updated. Notes are here.
The only Xen wrinkle is that you need the libc6-xen package. I don’t know if that’s in Feisty or not. In my case I experienced a slew of scary Segmentation Fault errors in the package configuration stage. I found :this post which contains a solution for the problem. But if possible you might want to try installing that package before upgrading. If that doesn’t work, just use the method described in that post.
After doing that and running dpkg --configure -a, it was okay. It did complain about AppArmor and being unable to do something with modules, but that seems to be not germane to Xen so I ignored it and rebooted, and everything seems fine.