I’ve abandoned Slack because of many of the reasons noted here. For me Slack caused as more problems than it solved. I’ve tried it with teams that used it too much (too many channels, too many splintered discussions, too much water cooler talk), to teams that just ignored it. For me, Slack was trying to solve problems I didn’t have thus it did not have a place in my workflow. The sudden embrace of it has been matched by its sudden disuse in my office.
Slack isn’t any more useful than any other group chat client. Didn’t keep everything in one place. Had/has the problem of too many people posting stupid chats that didn’t belong there.
In short it, like Trello or Basecamp (or whatever) adds a layer to the work process that has very little value over the long term. To date, e-mail, any old chat client, phone calls and/or walking over to someone’s desk continue to be the way we get things done.