Our PPM build server infrastructure has been very maintenance intensive; it needed some manual tweaking and fixing on a weekly basis. We finally couldn't stand doing it any longer and turned them off a couple of weeks ago. The PPM repositories are still there, but they're not being updated anymore.
But fear not! We took the time saved from having to do all the build monitoring and fixing and started writing a new simplified build system that avoids many of the problems the old one runs into.
More details can be found here.