Max Tegmark's article is illuminating and verrrry timely!
Until now, all the attempts to explain the alternative multi-verse views, that I have read, have been shotgun at best. They never before gave the reader an opportunity to "get their arms around" the subject. I've excerpted the Tegmark article now and again and have repeatedly referred Lurkers to it in various discussions here.
Personally, as a Platonist I am in agreement with the Level IV in Tegmark’s article. His frog/bird metaphor is superb for visualizing extra-dimensionality. Strangely, that helps also in understanding Burt Ovrut’s ekpyrotic cosmology even though the dimensions hypothesized are essentially parallel.