Electoral-Vote.com notes the following:

Stupidity news: One of Kerry’s electors in Ohio, Rep. Sherrod Brown, is a congressman. Unfortunately, the constitution forbids federal office holders from being electors. It is possible that if Kerry wins Ohio, Brown’s right to cast an electoral vote will be challenged in court. Whoever picked a constitutionally ineligible elector needs to get his or her mental software ungraded to the latest release.

Brown is indeed listed as a presidential elector: see here on page 11.
I assume that this would be an issue to be taken up, if necessary, in Congress when it counts electoral votes. I’d like to hear about any theories that could land this in court. UPDATE: A reader writes: “My understanding (from Rep. Brown