I have a cnps9500 and my computer is currently idling at 38-40degrees. The layer of AS5 i applied was VERY thin (ive heard too much negates its "wondeful" effects).
I would say my room temperature right now is about 68-70 deg F (with it being winter and all). If my room was considerably warmer, my CPU temp would obviously be higher.
However, i must say, I have yet to see a temp over 50 deg C (even after 3d marks cpu tests) with the zalman...so it works very well.
Other factors on temp include case clutter/ventilation, # of additional fans...etc.
I don't know if 68 deg temps are cause to go out and buy a new cooling system. Maybe reworking your current one can tweek it a bit. With my intel stock fan i was getting 55 degs at idle and 80 degrees at load....this i didn't like at all, so i got the zalman.