The buildbot now uses ccache, which sped up builds tremendously. Cycle time of build slaves with ccache using is 10-11 minutes; the e8400 and q9300 are almost as fast as the i7 now. (Dunno about the celeron yet.)
A few more flaky tests are now blacklisted, and the cluster has been running all afternoon without a glitch.
I hope to turn on email notifications sometime this week.