Checksums. If you rip the same track multiple times and the checksums are the same then you can be fairly sure you are getting an accurate rip. The completely paranoid can also check the checksums against the checksums that other people have got.

Even with my Plextor drive I found that on a surprising number of disc (and my CDs are well looked after) checksums varied on multiple rips.

Now that I don't have an external requirement for 100% perfect rips I would probably move back to Audiograbber if I got a faster CPU. Given that it takes more than an hour for LAME to encode a CD on my PC there isn't much need to speed up the ripping process.