We have branched our sources for 6.x just after release of 6.0, so we are working on new features for more then 2 months already, just integrating critical fixes into 6.0.x branch (that we release bugfix updates from).
During this time we started several new features some of which we are ready to announce today in the scope of the first EAP build. The main purpose is to let you know what we are working on and allow you to provide feedback early in the development.
We use fresh builds on our internal production server for several weeks already, so it should not have huge issues. However, there surely can be problems, so please use the build with usual precautions for trying preview software.
The first thing you notice physically about this lady build is a new color scheme and more lightweight style. I already leaked a screenshot back at RC times but now you can try it live for yourself. Love or hate it? Let us know.
Another important addition is preview of the feature to run a personal build in TeamCity for Git and Mercurial by pushing private branches to the server. This is the first time we introduce "branch" notion into TeamCity and it will probably develop into many more features in the future.
For other additions, please see the release notes or the full fixed issues list.
A note for planing your upgrades: we want to release TeamCity 6.5 sometime at the end of the spring.
Stay tuned to be the first to try the new features in the following EAP releases. You can not only try but influence them.