For those of you who use a wireless router and may work on one or two (or even several) machines in your computer room, an AP Client is a nice solution. When you move to another machine you can just move the wireless net adapter to the new machine and you're up and running on the network immediately. I've been using a D-Link G730AP for a while -- but it's not really made for this -- it's a pocket adapter meant to carry with you laptop. And, unlike my old Asus WL-330, it won't hook up to a switch.
Asus also makes a more powerful, larger, wireless AP/Client/Bridge/Reapeater, the WL-320gE. I bought two of these on eBay and they work great as Clients (network adapters) or "Stations" in Asus talk. They have a range of 850 meters (as compared to the pocket AP's range of 40 meters) so, in my room, I've got the full speed of my Cable wirelessly. It's three to four times faster than the D-Link G730AP, and it's solid (the D-Link was iffy). But, more importantly, I can hook it up to a wired (standard) switch and have as many simultaneous network connections as ports in the switch (in this case, four -- but I only use two). I've also set one up in the back of the house with a switch for my son's computers -- through several walls they're still getting very fast service. This is the only way I've used this device, but a lot of people buy them as repeaters. (I could mine up a repeater/client and my kids would have an even stronger single, but it's not necessary.) Another feature of Asus is that you can use it simultaneously as a bridge and as a wired client. It works well, the documentation is a bit inadequate, but it doesn't take long to "translate."
Anyhow, I've rambled again. The reason I bring this up is that these things are currently selling for $25 on eBay -- which is about the cost of mid-range USB adapter. The seller has nearly 800 of them. (I have no relationship with the seller, except I'm a customer.)
The eBay link is at http://tinyurl.com/ykysncw