After checking how fast the standard 1TB disk is I will likely get a 120GB SSD, I have made very good experiences with my current setup, having apps and OS on the SSD.
If you already have a system that has its OS and apps on a SSD, you can skip this task.
My OS and apps are on a 160GB Intel G2 and my bootable clone (via CCC) is on a 1TB WD Black (the same which ships with the Mac Pro, although mine is the 64MB cache version). Every time I have to boot from the clone to restore something, I'm glad having paid the 400 for the Intel drive. If you're used to a SSD, booting of a mechanical drive becomes just ridiculous. I really can't imagine working with a machine that doesn't boot from a SSD anymore.
No matter which type of mechanical drive you've got, the difference to a decent SSD is like day and night.
The Black drives are great for fast storage, though. Just a little bit too loud for my taste.