Edit after 1.3 official release:
Here is the announcement for the 1.3 release.
http://angularjs.blogspot.com/2014/10/angularjs-130-superluminal-nudge.html
It highlights new features such as
One-time bindings syntax, ngAria, ngMessages, ngModelOptions, strict DI and performance improvements.
There is also a migration doc to help with your upgrade
https://docs.angularjs.org/guide/migration#migrating-from-1-2-to-1-3
If your question is now “is it worth upgrading to 1.3 considering the massive changes planned for 2.0?”, I’d say the answer is definitely yes.
Orig answer:
Since you’re not asking about upgrading, I’m assuming you’re just starting development. If this is true, there’s a really good chance that 1.3 (or higher) will be the release version by the time you go live. So don’t hesitate based on it being in beta. Your code will be far less stable than the 1.3 branch 🙂
Also, they aren’t purposefully breaking things in IE8, they are just done testing that things still work in it. If you have a really strong business requirement for supporting IE8, then stick with 1.2. But even then, SPAs just really suck in IE8 considering all the UI fanciness that is usually required to make them usable.
Biggest reason to use 1.3 though is to avoid writing a bunch of code now that is for sure dependent on things that are already known to be a breaking change (because they have already changed).
To answer your edit, there’s nothing really notable or significantly new…
http://blog.angularjs.org/2013/12/angularjs-13-new-release-approaches.html
As a secondary goal, this release will cover features to improve performance, and small API fixes that require small breaking changes and removal of apis that were previously deprecated.
Edit 8/4/14:
It looks like they have decided to add something very significant to 1.3…
https://docs.google.com/document/d/150lerb1LmNLuau_a_EznPV1I1UHMTbEl61t4hZ7ZpS0/edit
July 28, 2014
Decided that we’ll back-port the AngularJS 2.0 Router to
1.3 in support of Material Design components.
The benefits and design for the new router planned for 2.0 (and for 1.3 it now seems) is outlined here: https://docs.google.com/document/d/1I3UC0RrgCh9CKrLxeE4sxwmNSBl3oSXQGt9g3KZnTJI/edit (in which they also have mentioned backporting to 1.x)