When I download Picard 1.1 and try to open it, I get this error:
"MusicBrainz Picard.app" is damaged and can't be opened. You should move it to the Trash.
This has something to do with Gatekeeper in Mac OS X 10.8 (and 10.7.5 I think, although not tested).
More info here: http://support.apple.com/kb/HT5290