Wired reports on a study finding hamsters subjected to jet lag suffered long-term cognitive impairment:

The jet-lagged hamsters were worse at learning which of two chambers contained a desirable running wheel. Even after 28 days of a back-to-normal schedule, the formerly jet-lagged hamsters still showed learning and memory problems.

At last, I have a scientific excuse!  Maybe we can all be more forgiving of our frequently traveling colleagues.

Or, here's hoping for a lack of external validity?