Glen and Leo bring up a couple of common objections to desktop gig, either users really don't need it or workstations don't have the processing capability to utilize it. (This is a bit of déjà vu, for those of us who experienced the 10 to 100 transition.)
On the "need it" issue, unless there's absoluting no benefit to the additional bandwidth, it might be hard to argue there's no need, although the cost vs. benefit issue is a different issue. (One of the biggest cost factors is the cabling plant if it doesn't support the higher bandwidth.)
As to host performance, providing better than 100 Mbps thoughput shouldn't be impractical for most recent vintage PCs. Any PC that can support USB 2.0 (480 Mbps), Firewire (400 Mbps), ATA PATA 133 (about gig) or SATA-150 (about 1.2 gig) with PCI 32-bit/33 MHz (about gig) or later bus architecture should have sufficient performance for a gig NIC. (BTW, a PC that has a disk drive that averages "only" 50 MB/s [400 Mbps], a 100 Mbps NIC is somewhat slow compared to it. A gig NIC would permit network I/O to match disk I/O performance.)
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BTW, I'm not suggesting everyone jump into gig to the desktop, just that it should be carefully analyzed for your network, both now and perhaps for a couple years out; whether it makes sense to start to provide it. Also, just as with 10 to 100 transition, not all users are alike. I.e., some, depending on their work, are likely to benefit more from gig than other users.
