Ever since I started my forum, we’ve had a topic Random Thoughts that’s open to all TLs. That has been used as chat by nearly everyone. Anything and everything is talked about. If a brief exchange relates to an already existing topic those posts usually get moved to that relevant topic, but not until the exchange is finished.
Some of my users have also used PMs (or DMs) for communicating between themselves things they don’t want in the Random Thoughts which is seen by everyone (even though this is a private forum).
On another forum, we have a group PM going each month with mostly Leaders and a couple of Regular members. That has been working great for us for over a year, especially if one uploads an image or photo, or links that get Oneboxed.
I’m not really sure how Chat would fit in in either of these two forums. Most of the users in the 2nd forum despise Twitter and have stated so several times. In addition to this, Chat would definitely NOT be an option for all users as it is a public help forum with a Help/Support category anyway. New visitors start new help topics.
Keeping with this topic title, you would have to think about what PMs have that Chat doesn’t - longevity, searchable, etcetera. And what Chat has that PMs don’t. Would giving up PMs really be good for your forum or not? Actually, you could keep PMs but push the Chat as the way to interact - until something needs to be taken to a PM… as long as PMs were still available. Thinking about our group PM on another forum, there is nothing preventing two or more from starting another PM to make discuss something brought up in the group PM or even to quickly talk about something completely irrelevant. In these cases there really is much difference between PMs and Chat. 