Now, dont get me wrong, it is a good product that I still recommend, just maybe not for Xbox 360 owners. Im not an expert in this area, but apparently the Play Link doesnt have quite enough bandwidth to download big files. It can send and receive smaller bits of info, such as during multiplayer matches, just fine, but when downloading big files it grinds to a halt and takes a very, very long time. I have never had any problems playing online while using the Play Link, so for Xbox or PS2 owners it wont be a problem. And even on the Xbox 360, it works perfectly for playing games online. But you cant download anything off of the marketplace unless you dedicated several hours to it.
Other Wireless Options
Not being able to download stuff quickly is a pretty big problem, so what are your other options if you want to connect your Xbox 360 wirelessly? You can use the official Microsoft Wireless Network Adapter but it will run you around $100. It works extremely well and is very easy to set up. For the record, this is the solution that I ended up choosing and I have been very happy with it.
You could also use the Linksys Wireless-B Game Adapter, which is quite a bit cheaper, but it can be more difficult to set up than the Microsoft adapter.
You can also use the Microsoft wireless gaming adapter from the original Xbox if you have it, but you have to have an original Xbox in order to configure it.
And if you want any additional information on wireless networking and how it all works, please check out About.coms Wireless Networking site.