1.) Beta V4, V5... - Large changes that require everyone to upgrade to use DarkSend
2.) Beyond this point, DarkSend is ready for real use and will be available in binary form (closed source still)
3.) Release Candidates - RC1, RC2, etc - I'll be taking bug reports, but these are smaller changes and none of them should require everyone to update
4.) First stable release - I think this stage should also be closed source until we're sure everything is perfect
5.) Public audits, where the closed source is shared with someone who people trust to review DarkSend (I'm not sure who that would be yet)
6.) After all audits pass and we have a real product, opensource
I think the audit should be that its opensourced after the last planned Beta, that should find any low-hanging fruit pretty quickly and would allow for yet one more beta to address those. Then a proper audit can be crowd sourced if the market desires it, like TrueCrypt.