Can you highlight a few of the reasons you love it, in comparison to HipChat? When we ended our trial month and announced we were going back to HipChat, the biggest reactions was "OK".
For me, there is also a bunch of minor detail where Slack wins. Slack just looks better, behaves better with choppy connections, and has better code pasting support. It also does much better with automatic link extraction (HipChat's Linky is annoying and won't let you remove the automatic description). Lastly, Slack has integration playbooks that automatically uses APIs to configure stuff or (when that's not possible) gives you the recipe; for example, the Github and Zendesk integrations will automatically register the app and webhooks for you, almost no manual setup needed. HipChat is all manual.
And for the love of God, HipChat, fix your inane emojis. Immature 4Chan memes (trollface etc.) have no place in a business, not even among developers.
Oh, they do. E.g. to make fun of those trying to look sooo professional.