I have a small LAN containing three PCs (two on Win7 Ultimate x64 and one on XP Pro), a Samsung network laser, and a Drobo box (with DroboShare).
At some point in the recent past (and I'm not sure quite when), it appears that sharing and device discovery across the LAN have stopped working.
I'm thinking that it must be either a Windows update or an AVG update that has changed something - other protocols seem to work OK (POP, SMTP, and some proprietary ones are all working).
It's not a general IP connectivity issue: all the machines can access the internet etc, and one another over different protocols (e.g. VNC and email protocols), it's just Windows networking that's failed.
All machines use DHCP but with IP addresses that are consistent due to MAC binding in the router.
All PCs are in a workgroup (one machine is XP, so we don't use Homegroup).