I upgraded from the first gen and yes, I am getting better signal strength with the 3gs than I did with my 2g.So you are getting better signal strength with your 3gs over your 3g?
I have 4 iPhones in my house. 2 3g and 2 3gs
The 3gs continually perform the worst no matter where I am in the uk.
For me I don't need any more proof and I stand by my statement that the 3gs has a poorer reception than the 3g. Unless of course I have TWO faulty phones.
Genius can run a test on the phone that shows signal level and dropped call log (the iphone actually logs data on this stuff). From that diagnostic they can determine if the radio in the phone is bad, requiring a replacement.