I've posted twice on this subject and gotten no response, but since we're touching on my exact question, I'll try again…
Before I upgraded the RAM in my April 2010 15" MacBook Pro/2.66GHz/Core i7/8GB RAM/OS X 10.6.8 (Build 10K549) from 4GB to 8GB, swap files would be created under what always seemed to be pretty odd circumstances, i.e. when I was either doing audio editing with Fission (most common), updating a CCC clone, or launching Safari with two or three multi-imaged eBay pages, but, without fail, when MemoryStick showed more than 50% of my memory as free, and no page-outs, and Activity Monitor showed "Swap used: 0 bytes". (I'd boot to one swap file, and see mostly one, but occasionally two, more created, but since I upgraded, I boot to one and stay there.)
The traditional wisdom that swap files are created when all available RAM has been used appears to be fallacious.
