>> Running 12V fans at 7V often works nicely (easily achieved with PC hardware by connecting the fan to 5V and 12V rather than 0V and 12V). <<
With my electronics-designer cap on, I'd advise a little caution with this. The 5V regulator is designed to source, not sink, current. If the fan current exceeds the current the 5V regulator is supplying (which is unlikely under normal conditions, but possible under stall or fault conditions), the 5V rail will go high and take out all hardware relying on it. One other possible problem is that a fan is an inductive load - you could be coupling large amounts of noise onto the 5V line. Summary: with small fans, it should work, but you've introduced a mechanism whereby a fan failure could destroy the machine. Steve http://www.fivetrees.com
