I stayed here the night before my Step II CS exam, which was about a 10-15 minute walk from the Cornerstone. The staff was extremely friendly and knew a lot about the exam logistics. They covered up the patch on my white coat for me, gave me snacks for during the test, told me what to expect, etc. They let me leave my suitcase there during the test, too.
Also easy walk to 30th St. Station to get trains, including the $7 train to the airport. Would definitely go there again if I was in Philly!