I went to PDC in LA last week and now when I get back home I find that I can no longer access some of my network file shares or ping certain computers on the LAN.  A few other people on some lists I'm on were having the same issues.  Apparently being at the convention and using its wireless had set our wireless cards to use Peer-To-Peer mode, and as such they were locked down.  One of these folks found the cure which is detailed in this blog entry.  I made the switch in my registry and it worked like a charm.  Try it at your own risk, of course.

In case that link dies, here's the important part:

You need to edit this key in your registry. Normal disclaimers apply if you don't know what you're doing.

DhcpNodeType should be 8, not 2, to enable broadcast lookups. You can release and then renew ipconfig to pick up the change.