Here are some of my problems I've encountered.

Track At Once / Burned on the Fly - Do not take advantage software 'features' that allow you to burn directly from MP3 to CD. They are no good, especially for bootlegs that should be DAO.

Incomplete / Mixed Shows - If you have an artist introducing the song at the end of one track, but then the EXACT same talk is at the beginning of the very next track, you have mixed sources... and it sounds idiotic. Even more annoying is that people always include 'extra' material at the end of a MP3 show to fill out the disc. Sometimes you cannot tell if this is part of the original show. (Other times it is so obviously bad, you wonder what the fool was thinking even including it)

Volume Levels - It only makes sense to make sure that the levels are the same for each track. Most people do not listen to music with their hand on the volume knob.

Digital Clicks / Partial Silence - Most MP3 to WAV converters will leave partial seconds of silence at the end of a track. If you do not remove this, you end up with a very loud & annoying CLICK inbetween each song.

Blatantly Bad Encoding / Decoding - If you don't have a good PC, don't be doing things while you are converting. Digital clicks / distortion is obviously VERY bad. Some people just don't seem to care. Use EAC.