No problem! I lived in Philly off and on (mostly on) for 5 or 6 years up until about a year ago. The 'grunge'/grime is probably a bit of a culture shock at first (depending on what you are used to) but it's a pretty nice city once you get over that.

If I were to move back, I would probably outside of the 'city' Philly along the main line. Lowest grime-factor there is, as far as I know.

Unless you've got kids or are going to school, I'd live in center city. For a fairly small and completely walkable area, it's got variety, from high rise apartments to "George Washington slept here" houses two blocks south. Best overall option in the city. Or live outside the city, but that's not living in a city.

Yeah, I'll be working in Center City and it seems like there are some nice places to live. What do you think about the area around Penn?

The campus is nice, but it'll push you west. Unless you're going to Penn, there's no advantage to living at, say, 40th and Spruce vs 20th and Spruce.

I walked all over the city looking at neighborhoods. If I were doing it over, I'd start at one river and walk down Market to the other, then back on Walnut, then back on Pine, then back on South. That's like 3-4 hours and gives a good feel for the area.