The good folks over at iLounge have run a number of experiments on the conversion speed and quality for converting DVDs to iPod format.
Their results? You lose considerable quality and it can take up to 10 HOURS for a 90 minute DVD.
From iLounge:
What do these findings suggest? Even on a good computer, converting videos for iPod playback is nowhere near as fast as ripping your CDs into iPod-ready music files. Techies will say “duh,†but first-time video encoders need to realize that under most circumstances, conversion from most unprotected digital video files will take at least two times as long as the original running time of the video, and quite possibly substantially longer – 10 hours is not unusual for an under two-hour movie. Two factors – videos with high frame rates and/or long running times – are most likely to drag out your encoding process.
Continue on to iLounge and read more about the DVD conversion tests.