Basically I've been playing around with Slack and it's kind of cool, but the integrations aren't very complete. There's a few things it does differently to Conpherence, mainly it has a concept of channels which are almost identical to the way IRC channels work (anyone can join or post in them).
It'd be nice to have this functionality in Conpherence (and then we can do things like synchronising IRC channels into Conpherence, etc)