The AccessAbility SIG has published information about Getting around at the 2008 conference in Philly. It has illustrated directions from the Market East Platform to the PA Convention Center or the Philadelphia Marriott. Also see the AccessAbility SIG's 2008 Conference Guide.
For those who are arriving by train at the Amtrak station, there is a note about how to transfer from the Amtrak station to the Market East station. Specifically, Amtrak trains arrive at the 30th Street Station, across town. From there, you have to go outside and down to the Market Street subway, or use the SEPTA (suburban) trains “upstairs” (actually up a ramp) to get to Market East (at 11th Street).
Whitney Quesenbery added that “These spaces aren’t that complicated, but they are cavernous, with passageways that are a city block long. If you are arriving on Sunday, it might be easier to take a cab. But be warned that on a weekday, you are crossing right through the heart of center city – so traffic is not fast.”
In addition, Marc Gravez, of the Philadelphia chapter says that finding the elevators is tricky unless you know where they are.