I went to Six Penn Kitchen a few months ago when the weather was still mild.
First of all, I love the location! I'm a big fan of Downtown Pittsburgh venues especially ones like this that have rooftop seating.
The food was great. I had duck which I never ate before this. I would not say that duck became my favorite kind of meat after this but it was prepared very well and the presentation was beautiful.
The staff was very attentive and kind. I had no problem getting sat along with my 7:30pm reservation on a Friday night I made via Open Table.
Parking is the only thing I really disliked but that is an overall problem in any major city.
I posted more about Six Penn Kitchen on my blog at http://midnightguru.com/place.php?id=73