I wasn't sure if I should create a bugzilla entry for this or not, so figured I'd ask first.
All I did was a zmcontrol stop, then a minute or so later a zmcontrol start.
Despite the clamd failed to start message, doing a zmcontrol status showed all services running fine. I'm able to send and receive email fine, etc.
zimbra@zimbra:~$ zmcontrol start
ClamAV update process started at Sat Mar 1 03:27:37 2008
WARNING: Your ClamAV installation is OUTDATED!
WARNING: Local version: 0.92 Recommended version: 0.92.1
DON'T PANIC! Read http://www.clamav.net/support/faq
main.cvd is up to date (version: 45, sigs: 169676, f-level: 21, builder: sven)
Downloading daily-5888.cdiff [100%]
/opt/zimbra/bin/zmclamdctl: line 62: 29587 Terminated
clamd failed to start
Not a big deal, but perhaps the root cause has other potential issues.