Count in another BMW driver who swapped to a Prius. My E36 325is averaged 20MPG when driving it as economically as possible, or 18 when enjoying its power. I'm still on my first tank of fuel from the dealer, in line for a 60MPG tank, whereas I would've filled up already in the E36.
I have found that cruise control helps my mileage. I have two theories on how it does this: (1) There are many very slight hills on my commute; so slight that I can't tell if I'm going uphill or downhill or level. The Prius can tell, though, and can adjust the throttle appropriately. (2) I don't have a scanguage and I'm terrible at driving with load. If I had a scanguage, I think I could improve that skill, but my foot isn't steady enough to hold a position up those long hills. In my experience, on my commute, I get about 2-3 mpg better using cruise than without.
