> Anyone got any clues?

I had the same problem with both the tlp and sip drivers using NetGear
cards.  They wouldn't communicate with anything on the network unless
they were running in permisc mode.  Try running tcpdump -i tlp0 in the
background and then go ahead and ping around.  When I tried it I would
have a ping session running and then quit tcpdump and the pings would
stop.  If i fired up tcpdump the pings would start once more.  I had the
problem with both a 1.5 GENERIC kernel and a -current kernel.

Tyrel