Actually there are surprisingly good quality "field recordings" out there, especially from taper-friendly bands. I've collected quite a few over the past year-check out my list for an idea what's out there:
http://www.tapercities.com/TheCrossroads/thump553/(the Patty Griffin I have is pretty good)
Some of my rough guidelines/rules of thumb for getting good quality recordings:
1) Stay far away from recordings that have ever been mp3'd. There is just too many crappy mp3s out there and people seriously interested in music trading just won't deal with them.
2) If you can find your music in SHN or FLAC or some other lossless format, I'd suggest grabbing that first. Its easier to make clean copies of computer files than audio files. Its extremely simple to convert from FLAC or SHN to WAV files for burning as a regular audio disc. If the person burning knows what they are doing, has decent equipment and is reasonably careful they can duplicate audio discs (essentially?) perfectly 95% of the time or better, so don't pass up audio discs completely.
3) There are excellent trading forums out there for Neil Young, Bob Dylan (probably the biggest and best), the Grateful Dead, Phish, etc., and tons of good mailing lists-Gene Clark and Roy Buchanan are two I participate in.
4) If you have a high speed internet connection, the BitTorrent method of peer to peer file transfer is an excellent way to get concerts-this weekend I picked up copies of a half dozen band's shows from the recent Bonnaroo concert. This only remain active for a few days, so you have to act fast.
5) The quality of equipment used by tapers, and probably their skills, have improved enormously in the past few years. Most recordings done now will be very similar in quality to commercially released live recordings-just less edited and no overdubbing. A recording done from the sixties or seventies, even a soundboard, can be quite acceptable but probably will not be quite as good as a more modern one.
6) Generally speaking soundboard recordings are superior quality to audience tapes (at the very least they don't have the problem of the drunken fool babbling throughout the show).
Let me know if you want any more info.