INTUI There is an issue up to version 1.2.2, due to a Mac OS X bug, which could cause apparently random crashes, it's solved in 1.2.3.
As for the main window issue, just click on the dock icon to have the main window reappear (as standard for mac applications), or use the related, configurable hotkey.
While no app is ever bug free, I haven't received reports about constant, heavy crashes, except for the above mentioned bug, so if you are esperiencing serious issues, send crash reports about them, as it will help a lot in solving pending bugs.
(Version 1.2.3)