I like Roll20 a great deal for online TTs but it doesn't strike me as really having the tools to act as a MU alternative at this time. The text interface is fine to capture play in a particular session, but saving completed scenes/subsequently linking them all together took additional work in gdocs or a separate wiki. You can run it alongside a MU client, of course, but once you're doing that I question why you aren't playing solely in the client or solely on Roll20.
All that said, I suspect the features it lacks are a matter of things not being requested/the developers not perceiving there's an audience for persistent text environment support, since it's mainly a TT session platform at this point. I value it a lot for what it is.