Ever since bug 541364 landed 4 months ago it's been possible to selectively disable platforms on try by overriding specific mozconfigs. Since that time, roughly 2321 hours (that's 96 days or 13 weeks or ~3 months) of machine time have been saved through this -- and that calculation is only compile time, even more than that has been saved on the test side. I just want to say a huuuuuuge THANKS! on behalf of RelEng. Taking the time to disable unneeded things on a push makes a noticeable difference in the time it takes us to turn around a full set of tests, especially during busier times. More stats:

• The most common platforms disabled were Mac 64-bit (115 times), Maemo (4: 115, 5 gtk: 106, 5 qt: 105), and Android (120 times)
• The least common platforms disabled were Windows (58 times), Linux 32-bit (85 times), and Mac 32-bit (96 times)