In my old 1999 SSEi the best I ever got was 31 mpg. Typically though I was seeing 24-26mpg.
One thing about Michigan -the gas there is considerably better than here in MN, which may contribute to the high window sticker MPG'* as Michigan is where the majority of the test'* are done. When Seth, Jason and I were heading up to Mississauga, ON in March Jason got 40 mpg in his 1993 Bonneville SLE (L27 3.06 axle ratio), and Seth got 41 mpg in his 1998 Bonneville SLE (L36 3.05 axle ratio).
So far in my 1998 SSE (L36 3.05 axle ratio) I have managed 30 mpg and with a CEL ( o2 sensor and another new code -unknown as of right now) I was still able to average 27.5 mpg on a freeway trip with 4 passengers (me being the lightest at 145 lbs). Now with a new o2 sensor I haven't checked the mpg'* yet, but the car idles noticably better and the gas guage isn't moving quite as fast.
And after Friday when I have my 3" down-pipe, 2.5" high flow Magnaflow cat, and 3" Magnaflow Wide Open muffler I should be able to get another 1-2 mpg on the freeway.