You, too, can have your very own vanity Arduino clone - I do

[dhouston]

If I correctly understand the Arduino Duemilanove schematic, merely removing the fuse in the USB 5V line means Vin will be 5V or 3V3 depending on which SMPS is plugged in and a jumper from Vin to the 3V3 pad makes it a 3V3 system. This also works for the UNO but it is impractical to replace the 16MHz resonator on the UNO R2. I'll need to use either 14.7 or 7.4 crystals depending on Vin. The Mega328P can run on even lower voltage than 3V3 but lower voltage requires a slower clock to reduce the current draw. I'll write up an AppNote for the ZBasic website explaining this hack. This is only applicable for those who want to use ZBasic for rapid development or who merely need to be able to choose 5V or 3V3 to match system voltage with various shields. It should be easily reversed by reinstalling the fuse and plugging in a 16MHz crystal.