After I tried this I didn't have single crash for over month now, before that it was either 1.5 hour idle game crash time or crashing to desktop after every 5th or 6th loading screen usually after switching from one char to another, hope it will work for you guys as well.
To enable the 3GB switch on Windows Vista™ or Windows 7:
1 . Right-click Command Prompt in the Accessories program group of the Start menu. Click Run as Administrator.
2. At the command prompt, enter "bcdedit /set increaseuserva 3072"
3. Restart the computer.
This has been working very well for me, though I consider it a 'work-around' rather than a 'fix'. I hope the devs can come up with a genuine fix for the underlying problem, but until then this allows me to enjoy the game better.
Update: Not a complete solution as the game crashed with the same symptoms after 5.5 hours play - but this is still a lot better than the 1.5 - 2 hours before.