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Same here. We started using Slack because it was the only thing that could break the use of ad hoc AIM and Google Chat accounts.

I do think that the Slack homes for user groups and open source projects (the ones set up with auto-invite on Heroku) are direct replacements for "join us on Freenode" invitations.

which, TBH, a nightmare, because within slack you need to change "group" to be able to be present in multiple projects, or join multiple slack-irc-server...

True, or Skype.

IM in a corporate setting has never really take off IMO. Email is usually the choice, which has a more mature in-house management model.

IM has massive deployments in big corporations. Part of that is that Lync/Skype is kind of a throw-in with Office/Exchange setups these days, but there are millions and millions of seats with IM clients running and being used.

We've got customers that are doing tens and hundreds of thousands of chats per day across their organizations.

I've seen Lync (Skype For Business) gain some traction in more corporate settings.

I remember using an IM client linked to lotus notes (was it sametime?) when I worked in a corporate setting 10 years ago.