TurningPoint has established itself as a major player in audience response technology, so you'll find a lot of support for it at Penn. For instance, SAS Computing has standardized on the ResponseCard system from TurningPoint because it is a good, reliable product. Although several clicker systems on the market provide very similar functionality, by standardizing on just one, they have built experience and expertise in supporting it.
Additionally, TurningPoint is under active development. They are now offering a product called "ResponseWare", which allows students to respond using a laptop or any web-capable smartphone. This can be used in a mixed environment, with some students using clickers and others using laptops/phones. SAS Computing has not deployed this yet, but if you would like to do a pilot test of this application, please contact them.