Question: Is there any way to tell whether a particular application running on Mac OSX (10.2+) has some of its memory swapped out (i.e., to one of the `/private/var/vm/swapfile*` files)? And how much?

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Answer: 
The `vmmap PID` command should give you some helpful stats in numbers about a given process.
As ridogi said, open Activity Monitor. Navigate to the process you want to inspect, and click... Inspect! Then click memory; this will tell you how much swap the given process is using.

Have fun!