I live roughly 20 minutes from Carlisle (just across the river from Harrisburg), rented an apartment in Carlisle from 1996-1998 before buying a house, and have work-related projects in both State College and Carlisle (Dickinson College is actually a client of mine). Everyone's opinions ahead of mine are pretty accurate, but I thought I could add a little.
Carlisle is a relatively distant suburb of Harrisburg, and while living there, I did most Harrisburg area-based errands and activities as part of the work day rather than get on Route 81 and travel northeast to H'bg. Carlisle has much better commercial facilities than it did in 1998; for instance a new Target now exists in Carlisle (and another brutal WalMart). The town itself has some good bars (Market Cross Pub - around-the-world beer menu with a passport) and Dickinson College adds some culture. The immediate Harrisburg area is ultimately still better for anything commercial or cultural though; both areas are significantly improved relative to the mid-1990s. I found that Dickinson's activities are generally unadvertised to the public, and even though living only a few blocks away from the campus, it was its own world. (I get far more Dickinson vibe from judging the science fair there and working for them than I ever did living nearby.)
The benefits of Carlisle relative to State College, I suppose, are proximity to the state capitol/sens and reps, courthouses/judges, and the overall political scene in Harrisburg. State College is a college town and only a college town. Overwhelmed with undergrads for 9 months and dead the rest; despite many grad students, it is an undergrad town through and through. Harrisburg has a (slightly) more mature social scene and a similar level of culture, albeit not associated with a college (not a bad thing at all). Oh, and nature is great in both areas - the Appalachian Trail is 10 min away from Carlisle and is the basis of many of my hikes.
I was even offered a job in State College at one point and chose to remain in this area just because, in general, State College is just more excluded from everything. It's all what you're looking for though of course...