The new Safari 6 Developer Preview that was available for developers shortly after the WWDC conference includes many new features from Safari 5.1 and 5.2. The move to Mountain Lion also means that Safari 6 is closer to the iOS version of Mobile Safari than ever before. Features such as iPad style tabs, iOS style expose tab navigation, and tabs that sync between iOS and Safari 6 are all welcome features being added to this version. Be aware that this is a developer preview so crashing will occur often and it is best to stay on Safari 5.2 which can be found here.
Anyways, if you want to give the new Safari 6 Developer Preview a try, you can download it from here. No guarantees of how well it will run on your system.
If you have any questions about the upcoming features of Mountain Lion, iOS 6, or Safari 6, please leave a comment below and I will do my best to answer your questions!