Very effective, and attractive too.
1.1 didn't seem to keep the preferences I chose, and I thought the scrolling screens was slower to use than tabs. But 1.0 is really nice.
May I suggest:
1) When you select a keyset from favorites, it switches back to the screen you were on previously.
2) You can set a default keyset.

Yes, 1.1 is very much a work-in-progress at this point, and definitely not ready to move up from extras-devel any time soon. The new combo-box mechanism to navigate panels is indeed slower than tabs, but does have the advantage of allowing many more panels. (I simply could not get the tab mechanism to work well when the tabs extended beyond the limits of the screen.) We'll have to see if there's a better mechanism out there for moving between screens.
Yes, a quick switch back from favorites to the previous panel would be convenient. Another user has proposed essentially the same idea, by making the favorites into an entirely separate window. I'll keep working on it. :) (BTW, you can avoid the favorites panel entirely by using the volume-rocker keys on the side of the N900 to step back and forth through your favorites list. This works no matter what panel you are currently using.)
I've set up Pierogi to store the current keyset when you close it, and start up with that keyset when you next open the app. But it shouldn't be hard to set up an explicit default keyset. Let me look in to it...
BTW, the TMO thread http://talk.maemo.org/showthread.php?t=82243&page=48 is probably an easier place to discuss Pierogi design issues. :)
Thanks,
--John