Real MPG varies
Well, the actual fuel economy you get will vary wildly due to terrain, driving style, temperature etc. I live in Michigan, which is flat (bad for the Prius which does better in rolling hills), has lots of 70mph highways, and has hot summers and cold winters. I drive the car like a normal car, accelerating at the same speed as the surrounding traffic, and driving at the same speed of surrounding traffic (usually a few miles per hour above the speed limit, but nothing wild). Occasionally for fun (and on seldom-driven roads) I'll play around and drive well below the speed limit, use an insanely light touch while accelerating, etc. - and that *does* make a HUGE difference. But, I'm not willing to drive 15 or 20 miles per hour below the speed limit or cause a traffic hazard as everyone behind me scrambles to try and get around me as I attempt to creep up to 25 or 30 miles per hour without the ICE turning on.
Over the last 19k (and some odd) miles, I'm averaging 43.3 miles per gallon in our 2002. I'm perfectly happy with that.
So, if you're going to drive it just like you would any other car, you probably won't get anywhere close to the EPA mileage estimates. If you're willing to drive it kind of strangely, then you'll get closer to the estimates. We have a lot of Prius owners out here, I usually see several every day, but it's almost getting annoying. I can't count the number of times a nice long line of traffic is forced to pile-up behind a Prius driver doing 55 on the freeway (which are 70 here in Michigan). Yes, it is completely within their rights to drive 55, but it is also a traffic hazard. You get a line of traffic flying past on the left and a huge line of cars all trying to get out from behind the driver clogging up the right lane. This last happened to me (once again) just yesterday evening coming back from some on-site work in GR (Grand Rapids). It's surprising how frequently the lead car in that clog is a Prius (I'm sure I just notice it more often because I drive a Prius, but the frequency seems disproportionately high). Yesterday is was a silver "classic" Prius just like mine - I literally blew past it doing 73, my guess is they were running between 50 and 55.
I'm also kind of worried that people won't realize the Prius can "do highway speeds" if people keep seeing them being driven like this. I get asked that question often enough as it is....
Oh, on a recent drive through Indiana on route 31 I consistently achieved mileage in the low 50's. Route 31 is a 55 zone most of the way though Indiana. I drove 58. If you live in a state that still has lots of 55 zones, you'll probably do GREAT.