.Net does have a pretty damn good GC. It is both a moving garbage collector (improves locality, reduces heap fragmentation and allows for memory allocation to be a single pointer operation) and a generational garbage collector (reduces garbage collection cost by leveraging heuristic that most collected objects are usually very young). I believe their server GC is even concurrent to avoid long stop the world pauses.
The problem is I'm not sure how much of those principles can be applied to D. I can see moving objects being problematic given that D supports unions. Another thing to consider is that .Net's GC is the results of many man years of full time work on a single platform, while D is mostly done by volunteers in their spare time for many platforms. It would probably require a lot of work to port, unless you're volunteering yourself for that work;) On a related note, I've wondered for a long time why D's GC isn't generational and why there's all this discussion on making it concurrent and none on making it generational. It seems to me that making it generational is simpler than making it concurrent and provides a net win in overall performance while concurrent only provides a win for real time systems that can't afford long GC cycles.
