Best place to intercept *all* DB calls

[eluser]jedd[/eluser]
I want to be able to make a log of all DB calls - probably straight to a text file, just using a couple of bits of session information (user, time) and the literal string made to the DB. So probably about 5 lines of code.

Where's the best place to put such an intercept?

JIC, would there be any change to the answer if I wanted to log to a DB table (still using the app's DB) instead?