How likely to work would a Jaunty-to-Karmic server upgrade, be?

[Harry Sweet]

I hope to find out tomorrow. I started the upgrade before I left work.  

Of course, I have a known working partimage-image so I can restore the existing system
in <4 minutes if anything bad should happen.  I know how long it takes because I borked
the server a couple of weeks ago trying to uninstall some weird software.

I would definitely recommend taking that precaution.  Check out the Linux Rescue CD

And oh, yeah, doing the upgrade will just upgrade the server.  You need to also chroot and 
ltsp-- help me with the command..  or the clients will still have the old sytem.