This is a site we read a lot in the Leafs thread, and it turns out they do MLS as well: http://www.sportsclubstats.com/USA/MLS.html
Clicking "Explain" under the rather depressing graph gives a very detailed rundown of how these numbers are calculated.
It's not often wrong for predictions, except for in the case of extreme outliers (the Minnesota Wild come to mind in the NHL).
Anyway, Toronto FC now sit at a 2.2% chance of making the post-season, 5.9% behind the Impact (can we even call them the Limpact anymore?).