I have Adobe Photoshop & Lightroom, Bridge, Premiere Pro, After Effects, Illustrator, InDesign and Dreamweaver CS4, as well as MS Office 2007, Sony Vegas Pro 9, DVD Architect and AutoCAD 2011, as well as a bunch of other video tools and film scanning software along with Windows 7 Pro 64 bit on a 120G OCZ Vertex 2. Even though all those programs take only about 43G, I wanted a little bit of "overhead" and some room to move.
I have always had my progams on the boot drive and my scratch discs and project folders on another "work" drive; a 1TB 7200rpm Western Digital Caviar Black. Since switching my boot/programs drive from a 7200rpm Seagate Barracuda to the Vertex 2, there has been a noticeable speed increase when working with the Adobe software. The programs open quicker for sure and going from task to task within the program are quicker as well. I think an SSD as an OS and program drive coupled with a fast mechanical drive(because writing to SSD's is a weak point) is the way to go.