The sticky thread with wheel weights lists the magnesium wheels at 24 and 20 lbs. The thread says those wheels were from 97-99, but I thought they were on later year vettes. Anyway, I just bought a set of magnesium wheels, 18x9.5 and 17x8.5 and I weighed them at 18.5 lbs and 16.5 lbs respectively. They are quite light. Perhaps someone else can verify this weight, and the thread could be updated.

I weighed the wheels three times and got the same result, using myself as a baseline, then myself plus wheel for the measurement, and subtracting the difference.