It's been a while... what kind of music was on mp3.com? Is this commercial stuff? Small bands?

All kinds of self-published stuff, lots of which later became commercial. You will have heard of some of it, for sure. Darude - Sandstorm? That was from there. DragonForce were big in the power metal category. The band that became Linkin Park came from there. And then hundreds of thousands of indie artists (including an earlier me).

The RIAA's action there destroyed vast amounts of music, pretty much the equivalent of if someone just aggressively deleted Bandcamp and Soundcloud put together and everything on it because they were upset they didn't control it all. I will never forgive them for that.

There was once a band called Hybrid Theory who had a name clash with another band on MP3.com at the time, so instead they called their debut album by that name. The band instead renamed to Linkin Park :)

(At least that's what I remember reading - the band certainly changed it's name from Hybrid Theory)

It was mostly indie bands and self-published stuff, at least when I used to use it. The idea I think was a place for legal music sharing without piracy. At some point it started becoming more of a web magazine thing and I kinda forgot about it.

it was essentially bandcamp before bandcamp