Going off on a tangent/rant here but I'll go out on a limb here and say that web chat is often (ab)used in a way that makes it the equivalent of global variables for communication: if offers the path of least resistance for sharing information (state) at the cost of making this information harder to retrieve, search, structure, associate, leverage in the future. Or to try another metaphor, it's the equivalent of dumping data on flat free-text files instead of a relational database.

Web chat does away with two (at least) properties I have come to appreciate in written communication: being asynchronous and contextual. Although modern web chat systems typically work even when you're offline by sending notifications, they're primarily a realtime system. There is the implicit or explicit expectation that a chat message (especially a direct one) should be answered asap, unlike an email or a tracker comment. As for context, there is little to none. In more than one company I've seen chat effectively replace the dedicated bug/ticket tracker system, with people polluting one or more channels with intermixed discussions that would be better off as comments on the ticket at hand. It's a mess for anything other than transient, throwaway stuff you wouldn't mind purging after a few hours or days.

Looking forward for a "web chat considered harmful" blog post if there hasn't been one already. </rant>