Bug 445611 is now resolved fixed, you can see the unittest results on all three platforms here: MozillaTry.
There are hopefully more machines coming that will be allotted to tryserver, with the likelihood that more developers will now use the tryserver. I'm also hoping to start working on setting up the web interface to allow for the selection of which platforms you want to try your patch on and whether you want unittests run or not since at the moment they are turned on for all patch submissions by default.
This patch also required the landing of a patch for bug 479225 where we now call the reftest/crashtest suites and the mochitest suites with make from the top level directory which helped us get rid of a bunch of extra workarounds we had to do for Mac OS since it needed to know which .app file to look for and we're changing that name so often (Minefield, Shiretoko, etc). Now all three platforms are even closer to being alike. Many thanks to Ted for making this possible.