We've updated our official download page with build 18130 which is stable TeamCity 6.5.6 release.
The version contains fixes related to IDEA and Visual Studio plugins, performance, Mercurial support improvements and more.
The same internal data storage format is used, so downgrade to any 6.5.x is possible.
BTW, we've got an IPhone app for TeamCity by one of our users. It displays last build statuses for selected projects. iOS 5 is required. You might find it useful if you often check how green is your project.