I recently moved to Philly last year to go to school at Penn, and I just picked up this guide on a whim. Boy am I glad I did! The reviews of the places I already knew were spot on, but more importantly, it tipped me off to some great places I had no idea existed. I found the reviews honest, concise, candid and often tremdously funny. And they thankfully suceeded to help me find a decent hotel for my mother to stay in when she came to visit. You can't bet that, nor can you beat the restaurant recommendations, which don't pull any punches.
One nice thing about the guide -- one of the things I noticed when I was trying to figure out which guide to Philly to buy, is that this Lonely Planet book covers neighborhoods like South Philly, Manayunk and Northern Liberites clearly, in detail, and with maps. As far as I could tell, no other guide to Philadelphia does this. Instead, they mostly deal with Center City. So if you want something that thoroughly covers the city, this is it.