Just to make things interesting, I too was recently hit by a memory leak. It wasn't the main program, though, it was calibre-parallel. And it wasn't on Windows, it was on Debian squeeze:
jim@sgtrock:~$ uname -a
Linux sgtrock 2.6.32-5-amd64 #1 SMP Sun May 6 04:00:17 UTC 2012 x86_64 GNU/Linux
This system has 4 GB of RAM, btw. The CPU is a quad core.
I had a hung magazine download going on for Cracked.Com, if that helps. It had been running for 627 minutes when I shut down the errant process. However, when I tried re-fetching manually, it completed just fine.