What absolutely killed HipChat for our team was the fact that its not possible to use HipChat for multiple teams. Need to be logged into multiple accounts at the same time (i.e your own team and your client's team)? Not possible.
Their suggested solution is to use multiple different clients (i.e. one native, one browser) at the same time, which is beyond ridiculous.
I dont think that I have seen any uservoice votes above 6000 for any other product request before (see http://help.hipchat.com/forums/138883-suggestions-ideas/sugg...).
With no solution in sight, moving to slack or flowdock was a no brainer.