Today, you can get gigabit switches at prices that drop the single port cost to less than $100. At that price, you can afford gigabit not just on the server farm but all the way to bandwidth hungry users.
Of course, you don't want to drop gigabit to everyone in the company. The port may be affordable, but you may need to replace your cable. If you already upgraded your wiring plant recently you may already have Cat 5, the minimum for gigabit, installed. But, if you last touched your cables in the mid-90s, you probably still have Cat 3. In theory, Cat 3's only good for 10Mbps Ethernet, but in practice, people have often forced 100Mbps Fast Ethernet to run over it. Well, sort of run over it. Ideally, you want Cat 5e or Cat 6 cable, since Cat 5 really is a minimum the same way that 128MBs of RAM is a minimum for Windows XP Pro.
In addition, the vast majority of PCs aren't fast enough to deal with gigabit Ethernet. A run of the mill cheap bus in a computer only runs at 133MBs per second, that's no where near fast enough to take advantage of gigabit's speed. Newer computers, using faster buses, like those based on Intel's 875P chipset, aka Canterwood, with 800MHz speeds can, in the current generation, deliver peak bandwidth in the 4.2GB range. That's more than fast enough to deal with gigabit Ethernet. In your servers, you may already have PCI Express (PCI-X), once known as "Third Generation I/O" (3GIO), buses. These can handle a GBps so they're up to the gigabit Ethernet challenge.
Still, the bottom line is that you're almost certainly going to need your upgrade your client PCs if you really want to get gigabit's speed benefits. If you can't, while gigabit Ethernet, will get you a performance boost over Fast Ethernet of about 30% on standard Pentium III and higher computers, it's not really cost effective since Fast Ethernet ports cost only a third of gigabit Ethernet's ports. Gigabit's much cheaper than it used to be, but then so is Fast Ethernet.
You should also be wary of computers that come with combination 10/100/1000 network interface cards (NIC)s. Just because the PC has a gigabit NIC under the hood doesn't mean the bus will actually fully support that speed. Buyer beware, if you buy PCs to use gigabit Ethernet, make sure the bus is PCI-X, 875P, or another high speed design. Just like computers with integrated graphics sound like a good deal, users who need top performance will find them ultimately disappointing.
No, if you really want to cost justify pushing gigabit Ethernet to the desktop, you're also almost certainly going to need to upgrade your PC base as well. If that's out of the question, you're probably better off waiting until your next PC mass upgrade and then putting gigabit in.
But, if you can afford to upgrade your client machines, putting in gigabit Ethernet makes a lot of sense... for some users. Even with today's low network and PC prices, there's simply no justification to bring gigabit to receptionists or word processors. Instead, you should focus on the people who really can use it.
And who are these people? The answer, as always, is to look at the applications. For example if you're using desktop video conferencing, the executives who actually use it should get gigabit. Other areas that will almost certainly benefit from gigabit are users who use desktop publishing (DTP), CAD/CAM, accounting analysis, database analysis, or graphics software.
The performance difference for these users can be dramatic. For example, a PhotoShop 6 image that takes tens of seconds to come up on Fast Ethernet can pop to the screen in a second using gigabit Ethernet. When your massive data file users make frequent saves, these time savings can add up to more than an hour a day, and that's impressive no matter how you will work out your return on investment.
As for the gigabit switches, you need to look for more than just maximum bang for bucks. If a switch offers you cheap ports, but does its TCP/IP switching in software instead of with an application-specific integrated circuit (ASIC), you've got a switch with a built-in performance problem.
You should also look for such features as authentication server support that works with your existing authentication framework. 802.1q and 802.1p support, which provides Virtual LAN (VLAN) and Layer 2 network traffic prioritizing for quality of service (QoS) respectively, are also important. And, as always, you'll want network management controls that you're comfortable with. Many switches, for example, now come with easy to use HTTP-based Web interfaces while others require you to know your way about a telnet character interface.
Concerns and all though, one thing is clear. At these prices, it's time to get ready for gigabit Ethernet. Maybe you can't afford it this year, but as PC speed increases and users try to do bigger and more data intensive projects on their desktop, you can count on demands for gigabit next year in data-intensive departments like engineering and DTP. Maybe with this economy you can't afford to implement gigabit yet, but it's certainly time to start planning.