I'd like to include them in the AAC CDs I put the childrens' playlists on, but our SONY car stereo doesn't do FairPlay. Of course I could burn a CD then re-encode the tunes to MP3 or AAC, but I'd tried that before and the results were awful. The re-encoded tune sounded like AM music (few remember how bad that sounded!).
This time, though, I'd try re-encoding at 320 kbps, no VBR, 44.1 sampling. I figured I'd also try the iMovie HD DRM removal trick. 
The iMovie HD trick turned out to be a nuisance -- I'd rather just burn a CD. Curiously, however, I got much better results this time than previously.
The original 5.6 MB FairPlay'd tune turned into a 52MB AIFF audio file which I then turned into two non-FairPlay'd AAC files:
- 128 kpbs (standard): 5.0 MB AAC (so smaller than the original - not good!)
- 320 kbps non VBR 44.1 AAC (max quality AAC using iTunes encoder): 12.5 MB
I don't know why I got better results today than in the past. Maybe last time I tried re-encoding as MP3, and the AAC to AIFF to MP3 transformations are tougher than AAC to AIFF to AAC. Maybe my ears are getting worse.
I wouldn't try it for Jazz or classical music, but at least some pop tunes survived the AAC to AIFF to AAC round trip better than I'd expected. I would favor a high bit rate for the reencoding though; I really don't have very good ears.
 The trick relies on a quirk of iMovie HD that is not present in iMovie '08. iMovie HD will export the combination of a FairPlay'd soundtrack and a JPG as a non-DRMd AIFF audio file.