With a bit over 2k miles on my 1LT/RS M6, my overall average is 21.56mpg so far (calculated, not from the onboard computer).
I'm tracking details for each fill up in post #5 of my car's journal:
http://www.camaro5.com/forums/showthread.php?t=31129
It seems as the though the v6 fuel economy can be fairly sensitive to your driving style. If I drive it as a Camaro should be driven, the average mpg will drop to 18'ish but drive it like a Prius and I've seen average mpgs upwards of 26-27 mpg in mixed city/hwy. Keep in mind, those numbers were from the onboard computer but were based on 50-100 miles of driving each time.