First off, your headline, "revolutionary," is factually wrong. Most of the base code is right from Thunderbird which is where some of the PB developers came from. They have added a lot of new features to it and have been good about support - until last month!

Im a long-time Postbox user, but I wouldnt switch to them now! The same time they lowered the price, they cut off all tech support!
http://support.postbox-inc.com/entries/21694767-how-to-get-help-with-postbox_forums
So, they tell us all to help each other, but they dont have the forum to do it in or allow us to post to their facebook page
http://support.postbox-inc.com/entries/21702158-where-are-the-postbox-forums
Ive now got 2-year-old bugs in their system that theyve closed and wont allow updating or entering new bugs. And, they havent responded to this in the last few days.