...well I just to need a little side note for myself ;-)

I have 4 Gb RAM, that's why I elected to "render in a separate process"...
at that point, on my 32bit XP I can use more RAM than would have if did not.

However, one may still want to keep the number of threads to 2 and not raise it to 3 if, like me, You want to do something else while You wait for the render (watch a movie, browse the web) without having the PC stagger too much.