While we're mostly at SLES11, we've still got 3 older SLES10 boxes currently out in the field due to lack of personnel and money.

We've had 4 SLES10sp4 servers over the past year and half just suddenly stop talking on the network due to xen bridge failing. Interfaces had to be deleted and recreated. In one case, there was no getting it working again, but fortunately in that instance that server could be replaced without losing a lot of data.
The latest incident was this past Monday. The host and guests were all up and responsive to keyboard input (after an hour and a half drive to test it), but the network refused to work.
Its like the bridging software in SLES10 Xen just disintegrates after about 5 years. Everything else is fine. Sometimes it's just the VMs that lose connectivity, though this last time even the physical host was inaccessible.
These are/were all Dell R710s.
SLES10 is now past EOL I believe, so any pointers would be extremely appreciated, as I expect to run into this again before we get those servers migrated. I've noticed SLES11 does it's bridging quote a bit differently.