The advantage of a MU* is that it is entirely text mode and rocks it 1990's style. I've had similar thoughts along this line but have never worked with the right group of people to make it so.
For those of you who don't know what this stuff is, it's a MORG, Multiuser Online Role Playing Game, only 100% text-based, and generally with a built in programming language of some kind. The basic client is simple telnet, though there are purpose built client for it on most platforms. They started in the pre-spam internet, back when Usenet was king.
The programming interfaces in these things can result in pretty sophisticated systems. Very common ones are bulletin boards and enhanced mail systems, just the kind of thing you'd want for status-tracking.
The commentor was probably thinking of the various rooms on a MU* as a way to handle multi-user chat. That would indeed be a great way to handle it. The room metaphor applies itself to meetings real well, and the text-based nature of it allows a complete transcript to be logged by anyone who is there; and also greatly facilitates the generation of minutes after the fact. It's a cross between IRC and IM, with the good parts of each.
Reading Jeff's post, there are a few things I am concerned with about the MU* model of project collaboration. First and foremost, unicode support is real iffy in the codebase for these systems, which could be a significant barrier to entry for non-english languages. Secondly, +mail replaces old fashioned email for only a few people, as it is restricted to inside the MU* system itself; programmers can't reorganize, resort, categorize, and file to nearly the same extent they could with a standard email client or Gmail. Finally, and perhaps critically, the entry line for these systems generally is interpreted (backslashes have to be doubles on some systems, semi-colons do strange things, that kind of stuff), which can seriously get in the way of discussing code-fragments of other languages.
Overall, I think it has potential for certain kinds of collaborators. It certainly isn't for everyone. I know one programmer in our office that won't touch a collaboration environment with a stick unless it has good UI (he has Standards), and this wouldn't qualify for him. Ones that are amenable are probably the kind that are already using IRC and mail-lists for collaboration.