We at WISOFT love Slack and have been using it for a while in many different companies. It's fast, safe and reliable tool for efficient team communication. We also use various Atlassian tools a lot and therefore a good connectivity between those two different animals was always a priority for us. There is a pretty neat, default JIRA integration available in Slack already that you can enable for any channel you like. However, it only works in one direction (JIRA to Slack) and it's a bit cumbersome when installing. Things getting even worse when talking about Confluence as there is no default integration in Slack at the moment.
We wanted to have a solution that works similar to JIRA's Hipchat integration, that is, allows us to link Slack channels to projects or single issues, create channels directly from JIRA, keep track of related discussions and be more verbose when sending notifications back to Slack. That is why we created our own Slack Connector. Not everything we planned is there already but it's plenty enough to make default JIRA integration obsolete. We had removed it from most of our Slack channels immediatelly after first release and hasn't been looking back ever since. And, we use it a lot for several JIRA projects, including Slack Connector project, of course!