Most, if not all, entry-level ADAs in Philadelphia start in Municipal Court. They're dealing with a ton of cases (mostly misdemeanors) and spending their mornings in court. Then, their afternoons are spent preparing the next day's cases. The weekends are used for catching up and clearing their desks ahead of the new week. I was a 1L intern there this past summer and worked on the same floor as the Municipal Court ADAs. They all seemed to enjoy what they were doing, but they acknowledged it was tough work.
I do not think that ADAs have this same schedule beyond their first year.
BTW, there was a profile of a new ADA in Philadelphia in the September 2007 issue of the ABA's Student Lawyer. Check it out, there is some great information in it.