I'm contemplating GigE. Like you, all I need is a switch. When I see
a deal I can't refuse, I'll jump. The rest of the infrastructure is
ready.

Well, a switch alone won't help you. It doesn't do you any good to have a
bunch of gigE workstations if you only have a single gigE link into the
server. It's often cheaper and equally effective to continue using
100BaseT/Full Duplex on the workstations and multiple connections into the
servers using 100BaseT or gigE. The key being able to get as much traffic
in/out of the server devices as workstation demands would require. None of
this matters, however, if you don't have switches that can truly handle that
sort of throughput. It's far better to spend your money on good switches
than it is to waste it on workstation cards. Fast cards ain't worth squat
if the switch can't keep up.