Another reason for 2 HDs
I agree that you can survive perfectly well with one hard drive. But having two IS a plus. In my case I have a 10 gig drive for the OS, and a Maxtor 40 gig U66 drive just for recording audio data. So my audio writes benefit from a bit faster speed.
The other nice thing about a second drive (and this gets back to Leolubin's question) is it makes system back ups easy. I use Norton Ghost to back up the C: drive periodically. It can write the entire C: drive to one big compressed file on D:, or (better yet) span it to multiple 650 meg files which I can then burn onto CDR. If my C: went completely dead, I could put in a new drive (any size as long as it was big enough to hold the image), boot up via floppy w/CD driver, and have my whole system restored exactly as it was in just minutes. You can use the same procedure to move your entire system to a new bigger drive.
Since my audio data files are just that, data, I write them out individually to CDR.
Incidently, if anyone is looking for a new system drive I see that Circuit city is selling Maxtor 15 gig 5400 drives for $75. Or if you prefer one big fast drive, several places are offering the new Maxtor 80 gig U100 drive (with free controller card) for $289.