On the second attempt, I remembered to turn everything off, and left iTunes in the foreground while it worked. When it was done, I stuck the disc in the PC (as it's the most finicky machine about reading homebrew CD's), and it didn't read. On the Mac, it read, but wouldn't play at all. Coaster #2, but this time, I didn't know why.
Before the third attempt, on a hunch I went into iTunes' prefs, and set the burn speed to 1x instead of 8x. I had already set the buffer to "large", so I left that alone. Again, I left iTunes in the foreground while it worked. The play list was about an hour long, and I left for about 45 minutes. I was surprised to find the disc done when I returned, so I can't really say it burned at 1x -- I need to do some further testing to see how fast it actually burns. When I tried this disc in the PC, it worked great ... it also works in all the players I've tried it in, so it appears I had a successful burn.
Pending further investigation, I plan on burning all my CD's in iTunes at 1x; it may be worthwhile (at least for those with G4/733 Superdrive machines) for others to do the same. Anyone else had similar or different experiences on similar or different hardware?

