A few have been asking about status when the dates bump, can't promise to make a post/thread every time in the future, but the current rebuild was for:
Bug 47686 - conversation navigational buttons missing in lite client
Bug 46538 - HTML appears in edit filter screen
Right now it's a matter of timing (also note historically we don't release on fri/sat/sun since less of us are around to assist). The thing to keep in mind every rebuild adds at roughly 2 days.
While we'll still push for 7th which we had targeted either (before those above bugs cropped up) that logic automatically makes it the 9th. We'll know more and firm up our guess at the end of the day. Yes I realize 31st was the old target; we strongly feel our triage/QA teams are doing a good job setting the quality bar high, even if it slips the date on ZCS 6.0.7 / ZD 2.0B3.
In the upcoming pm.zimbra.com re-design we'll try to include reasons as well as an rss feed etc. For now we'll try to note it in the small field next to patch/and include a reliability %, but the point it it's always supposed to be our 'best' guess; might add (and thanks to a few of you for noticing) we've been updating it the last few months early/often/pretty close to when the decisions are made.
To answer another question: We do have both a branch freeze to control variability (where only a dedicated release engineering team can commit code) and an internal target that moves around based on your demands - ie: What customers are clamoring about x feature or bug controls how strict we are in triage decisions (cutting/adding).