So, today I wondered what type of memory allocator OS X uses. So I looked around the XNU source code a bit, and found that it uses a zone allocator: there are 16 different memory pools (zones), each storing equal-sized blocks. Memory allocations are rounded up to a zone size, and a slot is popped off the corresponding zone like a stack. Each zone is protected by its own mutex. In other words, it's nearly identical to the allocator I want to implement, only it's semi-multi-processor friendly (due to the locks for each zone), as opposed to mine being completely lock-free (and thus full multi-processor friendly).
I suspect the Windows Low-Fragmentation Heap also functions like this, as well. Sometime I should reverse-engineer it to see if it's lock-free or has multiple locks (MSDN says it's multi-processor friendly, so it must at least have multiple zone locks).