I missed this post from Friday.
Mark Probst has posted a call for testers for Mono's new garbage collector:
Our new garbage collector, SGen, is now at the point where it's ready for early testing. It's still a long way from being ready for production use - it's still slow and consumes too much memory, especially for long-running processes - but if you'd like to help us find bugs, please consider giving it a try. I'm especially interested in cases where Mono crashes or hangs with SGen (other than for memory exhaustion). The simpler the test cases the better. To use SGen instead of Boehm, configure mono with the switch "--with-gc=sgen". At this point it's only known to run on x86 and AMD64 Linux.
This collector is a precise-heap, conservative stack, moving, copying collector and will return unused memory back to the operating system. The details of this collector are available in our Compacting GC page.
I am rebuilding my own Mono with Compacting GC now as we speak.