Anyone use custom router firmware?

[Sultan]

I'm looking to buy a wireless router, an ASUS WL-500G, which allows for downloading of torrents, etc. to network attached storage even when your computer is off. It is also compatible with open firmware for linux-based rotuers, such as the dd-wrt firmware designed for linksys wrt54g routers. Has anyone here messed with those custom firmwares? I know you can basically use them to turn your router into a mini linux computer. I'm wondering what all is capable, and how hard it is to install/customize.