Center City Philly Restaurant Week (really, 2 weeks) is September 12-17 and 19-24. Make plans to visit any of the 100+ restuarants participating this year if you enjoy the idea of a fine dining/McDonalds hybrid or if you find it amusing to watch servers dying inside as they struggle to please a screaming horde of diners who are all there because it's cheap.
Like Philly Beer Week(s), this event is a marketing vehicle that has ballooned into something worse than useless. What started as a good idea - serve a prix fixe menu of slightly smaller portions so that a wider audience can try a restaurant - has become something that people do because it's what a lot of other people do. Customers who appreciate good food can't enjoy it and don't get their money's worth, even at lower prices. Workers get screwed because every shift is like a double without commensurate tips. Maybe the restaurant owners see a bump in profits, or maybe these events persist because Philly has become "known" for them, and once we're known for a plausibly positive event (as opposed to, say, our murder rate or flash mobs) then we're stuck with it forever.
Anyway, my advice: Avoid.