To quote Unity’s website:
Unity 3.5 is one of our biggest releases to-date. It’s packed full of new features and improvements that we think you are going to love. We can't wait to see what you will create with it, so we've decided to open our 3.5 beta program to the public. Starting today, you can download a time-limited beta version of Unity 3.5.Some of those features happen to include a new Particle System (with Legacy particle support included, of course) and a built-in path finding system for Pro license holders (path can be run but not created under Unity Basic). They’ve re-written the occlusion culling system to allow for doors that open and close, dynamically changing the viewable areas, and has built in LOD support.
This release also provides a hands-on preview of Unity's upcoming Flash deployment add-on. Experience first-hand how Flash deployment in Unity opens up new publishing options, by enabling you to push your interactive 3D content to the web through Adobe Flash Player.
They’ve also added multithreaded rendering, which will give a performance boost on multi-core systems. To see all the new features, check here: link. Those of you who want to try the Flash should do it now, because once Unity 3.5 officially ships, you will be forced to upgrade and Flash support will require an additional license like the iOS and Android exports do.
Well, I’ll be playing on 3.5 Beta. See you soon.