Just thought I'd post a heads up that the WFT-E3a for the Canon 40D and 50D is starting to show up at fairly reasonable prices on the used market lately. keh.com had a couple of them for $450, and I just picked one up on eBay for about $350. If you find an older one and have a 50D, it just needs a firmware upgrade that is available for download on the Canon website. There isn't much to wear out on these things, so there isn't much downside to buying a used one and taking advantage of the depreciation.
Setting up the network to get the camera to talk to the computer was about a day long headache, but now that it's working, it seems like a very handy thing. I use the 40D mainly for copy work, so it's convenient to be able to see the image in real time on my screen and to fire the shutter from the laptop without need for a remote release to keep my hands out of the way of the lighting, and the images are stored directly on my hard drive.
It's also possible to do this via USB cable without the WFT-E3a, and USB is faster than wireless, but it is nice to have one less cable to get tangled or trip over, and to be able to change the setup or do a quick shot somewhere else in the apartment and have all the incoming images going to the same place.
It can also do other tricks like dumping images to a USB hard drive or flash drive, connecting to a wired network, and connecting to a GPS device and adding GPS data to EXIF, plus it's a vertical grip. I know some people are using these things with their iPhones as well.
I tell you, though, I'm such a habituated film shooter that when I opened the battery compartment on the WFT-E3a, by reflex I had a moment of panic, because I couldn't remember rewinding the film.