Zillow can be used as a general guide in neighborhoods where properties are all pretty much the same. What it can't do is accout for upgraded interior finishes, superior lot locations (like water front), home sizes (the s.f. counts are often not accurate and it often overlooks basements...an expensive "upgrade"). It also can't account for oddities in the market like distressed sales. A sale is a sale is a sale in Zillow. If you are looking for accurate home values contact a trusted Realtor in your area and have them prepare a CMA. An agent that is familiar with the area will be able to adjust for the nuances of the market and give you a good value range. Best of luck to you!
Zillow is a tool. It's information is often confused for fact. It is not. It is one computer's projections based on some data, tax assessed value, and other homes that are on the market.
As stated in Felix's response, your best bet is to get in touch with a local Realtor, and have them put together a price analysis of any community, to give you an idea of what the values of any property actually are.
Hope that helps.
Anyone with a computer and internet connection can be a Zillow contributor. If you're really looking for the true value, a REALTOR in your area is best. I tell friends and family not to look at Zillow at all. It confuses people - especially the homes listed "for sale." I'm sure some PA REALTORS will add more insight.