Okay, sorry if this question is completely stupid, but I couldn't get a straight answer from Google.
It's been over two years since I've upgraded my CPU. I just purchased an Intel Core 2 Quad 2.83GHz (Yorkfield fab) processor, and was appalled that it didn't come with any thermal glue. But looking instruction manual, the diagrams show to drop in the processor, and then put the heatsink on top without applying any thermal paste in between. Sooo... is it necessary? I'm not going to overclock it or anything, but I wouldn't rate the airflow through my case as stellar.
More aboutthermal paste
Brand new retail Intel CPUs include a HSF with pre-applied thermal paste. Thermal paste is absolutely necessary to fill the voids between the HSF and the CPU.