Over the last week, I've started using FastMM4 to improve the efficiency and track some leaks of a rather large program. On the memory management side, I've seen some nice improvements over the internal Windows memory manager we were using (we've stopped using Delphi's own memory manager some time ago). I've yet to do intensive testing on Linux.
On the debugging side, it is nice to have a report of left-over objects once the program terminates. As we avoid cleaning up at the end of the large program, reading this report is far from trivial.
Since the program makes rather heavy use of interfaces, activating full debug support makes it crash with additional memory errors a little too often. Of course this is making me worry about the code, although it might be that FastMM4 is a little too aggressive with its checks of formally incorrect situations that are practically harmelss in Delphi. I'll dig more and let you know.
I highly recommend this tool and plan to write about it soon (probably in my future Delphi 2006 ebook).