Quote - hey as long as I'm thinking about it, what's the difference between hardware accumulation buffer and software accumulation buffer?
Sounds to me like the video card RAM will be used  more in hardware accumulation, but software accumulation...
I have no idea what those settings do.

An accumulation buffer is generally used for things like antialiasing, motion blur, and depth-of-field effects.  I can't tell you much more than that, unfortunately.

I really should run a few tests sometime, alternating between hardware and software modes, to see if there's any significant impact on preview performance.