I do like the idea of replaying logs as performance tests, this got me thinking:
http://www.igvita.com/2008/09/30/load-t ... og-replay/

When Steve Hedley and I did the ATM Service Management system performance testing, we took a recording of the service requests set by 7000 ATM's, parsed them and scaled them up to be 20,000 ATM's.

Record live system log, then tweak it to be input to a test system performance test.