I'm a 4th year at Penn right now and, like everyone else who posted, think Penn is a fantastic program. If it was in any city other than Philly, it would have been my number 1.
I did a ton of different rotations here and thought they were all great. One of the best for an away rotator, though, is probably the combined Neuro-ortho/Sports rotation. Not only is it a great chance to see procedures you will not see very often (at least on the Neuro-Ortho side) like Girdlestones, SPLATTs, etc., but both attendings you will work with (Keenan and Sennett) are top-ranking members of the Executive Committee (i.e. the people that make the rank list). That said, Keenan pimps a LOT on anatomy, so make sure you know your stuff before you start.
The tumor rotation is also good--awesome cases!--but, at least from my experience, you will get only a limited amount of face time with Lackman.
Hope this helps. If you have any more questions, feel free to PM!