Same issue here. I was able to reboot my 10.7.1 server without issue (SMB connections would work fine).
However after applying the 10.7.2 delta server update via Software Update, SMB was open, but nobody could authenticate to the server (Mac or Windows using SMB).
Having to stop/start smb has temporarily resolved it.
I haven't rebooted the server again (yet), so I don't know if this is/was a one-time issue related to the upgrade process or if it's now a every-time-you-restart issue.
I would agree it may be a hardware-specific issue. The older core2duo Mac Mini I use for testing server does not show this problem. My production server (a current-gen MacPro) showed this today.
THAT SAID: 10.7.2 fixes the need to prefix the user name (on Windows) with the server's netbios name!
I can now log into my server from windows with "maser" instead of "<netbios>\maser" again! (Though the prefix still works, too...)