[netcraft]

I think Slack serves its stated purpose very well (smaller, business oriented teams), but many groups have started using it for larger communities, mostly because it has unlimited users for free. But it isn't made for that and there is no way that most of these groups would ever be able to pay for a premium subscription due to the per-user costs. 10K messages across all channels is surprisingly easy to hit, need the ability to ignore users, etc. I think this project has great potential to fill that niche if it is marketed properly. Slack is so close to working well in that area but really needs to pivot to be able to serve it well and make money doing it.

[g4k]

Yes, recently Slack even told Reactiflux that they need to move to another service as more than a few thousand users can not be handled by the Slack infrastructure.

[silentrob]

That isn't true. My office slack has a few thousand users and it works just fine. I'm not saying it can scale to infinity, but it does handle a few thousand users without any issues.

[detaro]

I have no clue what the exact numbers are, but apparently it is an issue:

http://www.reactiflux.com/