As ts been mentioned a few dozen times, most of the real world difference between a 320GB 7200RPM and a 500GB 5400 is going to be in the user's head. I'd be more concerned about how much cache.
It may very well be in my head, however, as far as the cache is concerned, the 500G 5400 RPM Scorpio Blue is 8MB and the Seagate 500G 7200 RPM offers a 16MB cache. That's enough to convince me that it's probably worth the wait since I need it, but can survive without it a bit longer. I won't be terribly surprised (although I'm sure I'll still be disappointed) if next Monday comes and goes without my drive being shipped; but again, I'll deal with the wait. I think the extra speed, imagined or not, will be worth it (not to mention double to cache).
P.S. -- pdxflint: That was a nice article on the Scorpio Blue; I hadn't come across that before. It looks like it does compete very well with the other drives. As you said, it didn't compare it with the 500G 7200 RPM Seagate, but it was compared with other 5400 RPM Seagates and other 7200 RPM drives. I must say, I'm impressed. If things don't pan out with the Seagate I've ordered, I may have to reconsider this drive a bit more seriously (had looked at it briefly but dismissed it without much research because of the speed & cache). I'l definitely keep this one in mind. Thanks for the link; it's a great read.