NEVER turn it off. It's the best feature of the processor. When you run more than one task or others, say norton run in the background. It doesn't affect your work, no slowdown.
I can run two folding programs at once, download things from the net, scan my computer and play Farcry at the sametime. SWEET
Intel Core2Duo 6400 @ 3.4Ghz
4GB Geil 6400 Ultra
3 x 500 Gb Samsung HD
EVGA 8800 Ultra OC