The only drawback I have found is that iTunes does not offer a scroll option for the comments box ... time to e-mail Apple.
[robg adds: Keeping lyrics directly with the song is a good idea. Unfortunately, Apple's comment box is basically brain-dead, so you'd have to copy and paste them elsewhere in order to really read them easily. Perhaps the comment box contents could be AppleScripted, though, to automate the extraction process.]

