Here's the setup: my OS is installed on a 60G SSD. It is replacing a 40G SSD -- 40G just wasn't enough space for the OS partition because of the 8G of RAM in this system. Question is, would keeping the 40G SSD and putting the swap file on it improve speed? I'm thinking it might because that would be two SATA channels instead of one. E.g. when accessing a program on the 60G SSD any swap file access would go thru a separate SATA channel. But I don't know enough about SATA to say that this would be a speed improvement.
Update: Tested this with SiSoftware Sandra Physical Disks test.
Before (40G SSD only): 200.60MB/s
60G Vertex2 only: 202.09MB/s
60G Vertex2 + swap on 40G Vertex: 226.83MB/s
So a 10% performance improvement from placing the swap file on the secondary SSD. All told, not that impressive. It might be worth putting the "Users" folder on the small SSD and the Windows partition on the larger SSD.