This build #29939 is a bugfix update for the recently released TeamCity 8.1. It comes with almost 80 different fixes for both issues introduced in 8.1 and long-standing ones.
Check the upgrade notes and get the build.
This update uses the same data format as 8.1, so you can downgrade to 8.1 if you feel the need.
Also, the upgrade is free for those who runs 8.1 (maintenance period of the licenses covers 12 February 2014 - 8.1 release date)
We will continue to release bugfix updates as issues uncover but our main effort is getting switched to TeamCity v.next which we plan to release to the end of the year.
Next week the team will spend some time in discussions about new features and directions we will pursue. Since these will partially be held offline, we might delay with the answers in support email. Hope you understand.