Do people still use Zip drives?
Really. When you can get CDRs for less than 1¢ apiece, why not just burn a CD real quick?
The only valid reasons I have heard for a second internal drive with external access is:
1) CD-RW, so you can do disc-to-disc copies
2) Faster CD-RW, so you can burn CDs at 52x instead of 16x
Both of these are valid complaints IMHO. I don't think that (1) is a big deal for most of us, since you can make a disk image in toast on the rare occasion that the average person would do this (pirates excepted of course). (2) seems like a complaint I might have, but I don't know how fast a 16x SuperDrive burns a CDR, so I can't say. If it's 4 minutes or less, then I'll have no complaint (my $20 52x CDRW burns 700MB in about 3 minutes).
The bottom line is you have to go with an external Firewire unit if you need another media drive.