When I upgraded an Ubuntu system within a VMware Server instance, I found that the VMware Tools provided by VMware Server 1.0.5 do not compile against kernel 2.6.24.
However, there is a solution: With patches from tuxx-home.at, the vmxnet module compiles smoothly.
Yesterday I upgraded the Xen Dom0 hosting various DomUs (for example my Jabber server) from Ubuntu 7.10 to 8.04. However, after upgrading Xen stopped working.
I tried to use the old 2.6.22 kernel instead of the new 2.6.24 one, but no chance. Xen did not show any error messages and started the DomUs, however neither networking nor "xm console" were working. In fact "xm console" did not show anything and did not react on keyboard input and even a SIGTERM caused no effect. I had to kill the instance with a SIGKILL or SIGHUP.
Now, after I have restored a backup of the old system, everything is working fine again. Therefore I advise everyone using Xen on Ubuntu not to upgrade to 8.04. Upgrading the DomUs however did not cause any problems, Ubuntu Hardy Heron seems to be broken for Dom0 only.