ATtiny25 Basic VCO, RC oscillator overclocking and testing frequency pickup

Alex over at InsideGadgets has posted an article describing how he built an ATtiny25 voltage controller oscillator (VCO):

I recently bought a Rigol DS1052E and have been playing around with the different functionality it has. Eventually I came to the point that I’d like to see what frequency does to various components and wanted to build a voltage controller oscillator (VCO).