According to a thread in Apple's Discussions forums, some users are experiencing crashes in iTunes when iTunes connects to the Gracenote CDDB (CD database) to obtain CD information. The behavior started yesterday (Tuesday) evening, and, interestingly, only appears to occur with certain CDs.
We haven't experienced this issue ourselves, but if you are, disabling "Connect to internet when needed" in iTunes preferences will at least keep iTunes from connecting to the CDDB (and will thus prevent such crashes). The downside is that you lose the ability to automatically retrieve CD information.
If you have resorted to this temporary fix and want to get CD information, two posts in the thread referenced above offer potential workarounds. The first is to import songs off of your CDs, and then select them in your iTunes Library and choose Advanced -> Get CD Track Names. The second, if you happen to have Roxio's Toast installed, is to launch Toast and choose Copy CD mode; when you insert a CD, Toast will access the CDDB (apparently Toast isn't affected by the glitch) and save the song info to the same local CD information database used by iTunes. When you switch back to iTunes, the song information will appear.