I would say you can slack off on case fans, but CPU fans are ABSOLUTELY necessary. Even when idle my AMD Duron spits out a lot of warm air with that fan. Warmth that would otherwise remain around the heatsink, or worse, around the processor.
If you don't like the noise you could always try buying another fan (I am looking for a queiter CPU fan myself, and I think volcanoes tend to be loud) but you have to have A fan on there.