I usually use about 25 to 30gigs for a project. I can suffice on 6 to 12gigs if I plan the vid out in advance. I like to have 60gigs available, but that doesn't happen often.
I wouldn't mind picking up another external harddrive, but I'd only use it to store things so I don't have to burn dvds as often. The only way another harddrive would affect my editing is that it would let me procrastinate more instead of cleaning my drive off every few weeks.
/random
Here's one for the smart people. Why do my 60gig + 250gig drives add up to 288gigs in "Total Size"? What happened to the other 22gigs?