ZCS 4.5.0 GA was just posted. It has over 90+ new features as well as 1000+ bug fixes.

A few of the new features include
- Mail Identities
- Personal Distribution Lists
- Complex password enforcement
- Zimlet management via administration console
- Zimbra basic html client

Full release notes will be posted soon. The complete list of fixes and enhancements can be found in bugzilla.

Also Ubuntu builds have officially become GA.