M3i zero and Datel Games n Music(I dont think it even works anymore, but since I no longer have my phat I cant really test it)
Used for all of the above - piracy, legal backups, homebrew. I use it for media a bit, but not often due to the DS being a clamshell and therefore not a good form factor for that sort of thing.
I went from a DS phat to a DSi, and I'm finding its completely worth it. however, if you have a lite I'd hold off unless/until it gets its own proper homebrew, in which case I think it would become a must buy.