Ok, after extracting about 150 cds, I realized that I had not enabled DMA. My question is, how bad is that? Does that mean that the audio quality of the ripped tracks is suspect? Do I need to re-rip those same cds if I want to make sure they sound top-notch?

Depends on many factors (does CD-ROM drive have hardware jitter correction, is your ripping program paranoid enough, how fast is your computer, did you do something else while ripping etc), but I don't think you will have problems because of lack of DMA. I would check a few tunes, and if they are OK, say 'what the heck, I will upload them and re-rip the bad ones as discovered'.

The only thing enabling DMA will give you is a faster rip speed. Maybe.

You should already have been listening carefully to your ripped tracks to make sure they do not pop, skip, or have stereo channel problems, as outlined in the FAQ. So if you listen to the tracks and they do not have any of the characteristic "bad rip" problems, then you do not need to worry about the audio quality.

DMA won't help rip speeds since the PC's bus isn't the data bottleneck... the CD drive ripping the data from the CD is. Besides, all DMA does it take processing overhead off the CPU since the CPU doesn't have to handle data transfers around the system anymore... the DMA controler does that.