I also have a Prius (2005 model), averaging 48-50 currently. Over the summer I can routinely hit 53 with about 40/60 city/highway driving.
All those people who complain about the Prius not hitting its EPA estimates just don't know how to drive smoothly. The 60mpg city rating is far too optimistic, but the 51mpg highway rating is also rather pessimistic. The 2008 ratings are just stupidly low. I live in hilly New England. When I took a road trip to the flat midwest last spring, I was doing 56-57mpg on the freeway.