Ripping all my CDs onto the thing so I could change the soundtracks on the GTA games, and DOAX (which was legit fun back then, with a surprisingly detailed playlist editor).
It was my unofficial Dreamcast 1.5, when Sega dropped outa the console business I went straight to Xbox. Had great times playing the Rallisport Challenge games, Buffy, Shenmue 2, all the DOA games, and the Balder's Gate DA series with roommates. I ended up modding the thing a few years later and made it a media hub for a while, and I could install my games on a larger HDD.
I still have the Xbox, but it's dead. I think it was that capacitor thingie, I never knew about it.
Oh yeah, and Bioware was awesome back then. You knew you were in for something special when you saw their logo.