I installed PA on my Nexus 10 a couple weeks ago, and after enjoying having the tablet UI back for a few days I tried out PIE.
It works pretty well, and I really like that it frees up the bottom of the screen where the nav bar normally resides. I have a couple thoughts on how it could be improved.
1. Pie Gravity: I'm currently using the pie anchored to the right edge of the screen, and this mostly works well, however it interferes with a few apps that have touch screen gestures that involve swiping in from the right edge of the screen. I would prefer to trigger the pie by swiping up from the bottom, but this causes the pie to appear in the middle of the bottom edge of the screen, which makes it difficult to reach all the options while holding the tablet in landscape with one hand on each side. I'd like the pie to appear in the lower right corner. It would be nice if the pie would appear near where the swipe that triggers it occurred. Or, failing that, if there were an option to specify in a little more detail where the pie appears.
2. I'm currently using the pie along with the phablet status bar by setting my nav bar to 0. In this mode you don't get the full functionality of the pie (with time battery and notifications displays). This makes sense most of the time, however a few apps (most notably lots of games) disable the status bar while in the app. If I want to check the time or battery status while in one of these apps, I have to switch to the home screen so the status bar reappears. It would be nice if I could just swipe open the pie while remaining in app to check those things. I'd like to see an option to enable full pie functionality when not in expanded desktop mode.
All in all, excellent work, and a big thanks to all the PA devs.