I've got the Pioneer DVR-109 in my B&W G3 and it works great. A LOT quieter than the 108, which I had previously. Both GREAT drives. And both are 16X and Dual Layer burners. The 109, though, is faster on DL burns and normal CD burning.
Just download Patchburn 3 (i think it's 3) and run it and reboot and you're all set. iTunes, iDVD, etc. will all see it as a "Vendor Supported" drive and will burn just fine.
If you buy one though, and you or a friend have a PC, I'd suggest installing it in their system and flashing the firmware to the most current in either drive, and then popping it in your Mac. Pioneer doesn't make a firmware updating utility for the Mac. The earlier firmware didn't allow certain speeds for burning/reading. There is a flashing utility for the Mac, but I've never had any luck with it.
And, if you've recently purchased a PowerMac G5 (since around November, I believe), you already have a DL burner, Apple just hasn't "activated" it yet. The Pioneer DVR-117D that is installed in a G5 are actually just Pioneer DVR-108 drives with firmware that limits the burning speed and gets rid of the DL functionality. I haven't tried it with my G5 yet, but some people said they've had success with the firmware and now have a lovely 16X and DL burner in their G5.
OWC has some pretty good prices on bare drives, and if you want some extras thrown in with your purchase, they have some bundles for a bit more.
If any of you have any questions on either of those drives, let me know, I'd be happy to help.
enoch