Given that I started using Slack (slack.com) last week, what in Hum would tempt me away from it? Slack fits pretty much everything I would want in team communication (being more or less private IRC with persistent history, full history searching, file uploads, etc), and has straightforward APIs and preexisting integration with assorted software and services.

The only thing I'm seeing Hum offer that Slack doesn't have any equivalent to is the email integration, and if I'm emailing somebody external to my team or company I'm not going to want to treat it like a chat anyway.