Congrats on the Prius, it really is an amazing vehicle right out of the box. Of course its still fun to play with it.
If you were getting 30 mpg out of your Subaru you shouldn't have much trouble hitting 50+ with the Prius, especially in summer.
I would suggest getting a scangauge II. The info it provides along with the x-gauges are quite helpful for driving the Prius and giving you more info to work with.