Major Highlights:

John Zeller made it possible to trigger builds/tests on arbitrary revisions. This is a feature with HUGE impact -- it will allow us to bisect problems much more easily, and possibly even do so automatically.
Kim is happy to be back from parental leave and has been preparing to spread the word of Mozilla RelEng to EclipseCon next week and at Google's RelEng Workshop in April.
John Hopkins has been continuing his work on helping get tests on 64-bit Windows EC2 machines green, which will help us scale to the cloud for those tests and gets us closer to shipping a 64-bit Windows binary.
Armen enabled mozilla-inbound desktop browser-chrome and b2g reftests on EC2 test machines. While they're still hidden for now, it's gotten us much closer to making sure we keep turnaround times great for those tests.
Catlee figured out that l10n nightlies were a big part of the reason we've had tree closures due to pending jobs, and we've moved those builders to jacuzzis to fix that.
Taras and Rail wrote a better algorithm for bidding on EC2 spot instances. Because of that we're now running more jobs than ever on spots, and well under 1% of them are killed off because of a higher bid.