It appears we're both right, well, at least according to Wikipedia, the source of all truth and knowledge! There are two "kinds" of pounds, pound force and pound mass. I had only heard of pounds as a measure of force, and did not know they were officially recognized as a measure of mass as well. Those tricky pounds.
Huh, so I guess PSI would be "pounds force"? And you're forgetting the other two kinds of pounds: pounds-currency and pounds-forehead-because-all-recipes-are-in-bizarre-archaic-units. 
Yes, PSI would be pounds-force because pressure is a force distributed over area. The unit of mass that was normally associated with "pounds-force" was a slug (which was the amount of mass that would accelerate at 1 ft per second squared when 1 pound of force was applied). So, I suppose we could talk about how many slugs we should put on our cheese? Hmmmm, perhaps not.
- Jeff
