I'm currently snagging the first 500 songs through BitTorrent. VERY SLOWLY. It's averaging about 8 bps or so. Usually it's sitting there stalled for one reason or another. I'm not impressed with BitTorrent or the current crop of p2p software..
Here's a basic rundown of what they're for:
BitTorrent: Movies, games, big stuff (I've found PS2/XBox ISOs there too). Theoretically it's very fast, but I've never found it to be. Drawbacks: Major corruption. Download speed seems to depend on the number of people currently downloading, not the number of people who have the full file.
eMule: Movies, Games, just about any software, properly-implemented MD5 sums mean flawless downloads every time. Drawback: It can take a few hours or days for a file to get up to a solid download speed (depending on popularity).
SoulSeek: This is the one you want. Designed for music, and it doesn't download the same file from multiple users at the same time (no corruption). You can even download entire folders. Another benefit is that it has some very rare MP3s (stuff I've never found elsewhere).
Of course, if none of that works you can always get these MP3s straight off OCRemix's website.