Microsoft (at least for win7 and win8) releases their beta's for free to anyone who wants to download it. I can think of two main reaons and possibly a 3rd for beta's to exist. 1) For developers to test their apps in the new OS 2) To be guinea pigs to allow for sufficent bug testing And the possible 3) to get advanced feedback/suggestions regarding any changes Reasons 2 and 3 would be further helped further by the more and more people who use it. I'm sure some of you will respond something along the lines of "The last thing we need is the general public complaining about how buggy it is or screwing up their computer etc etc" But I think that if someone takes the effort to go to Apple.com and download this clearly marked "BETA" operating system they are sufficiently geeky enough and/or know well enough that it is a beta system and to expect many problems. If it screws anything up I'm sure it's a pretty simply process to remove the Beta (and redownload if you wish). I'm assuming to download ML you partition your hard drive (a la boot camp) and then you can dual boot into which ever OS you want?