I'm kind of keen on doing something similar to this, and have thought about it extensively. I'm really only going to be building a speedo though.. but I've had a couple of thoughts you might consider:
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Touchsense/Capsense is MUCH harder to implement if you are wearing gloves. I've had a crack at this and it's not worth considering I reckon.
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Accelerometers are also quite hard to implement with lean-angles as there is v-little lateral force due to cornering if the accelerometer is fixed to the bike. Depending on where the acc is mounted along the 'north-south' axis of the bike, all the forces due to cornering will be directed down through the Y-axis. You COULD calculate it using vector geometry, and I managed to using a Nunchuck, but it's still quite tricky.
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Gear indicator is easier to implement if you are reading both speed AND tachometer values. Just have some sort of calculation... if you are doing 100km/h and the RPM is 2000RPM, the you're in 5th. If it's reading 3400RPM then you're in 4th etc etc.
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Thought of using something like a PS2 controller, or Wii Nunchuck (which is i2c!) which has the analog joysticks on them/it? Waterproofing it would be tricky, but how cool would it be to have a PlayStation controller on your bike?
Looking forward to hearing more about your trials. I'm doing this from New Zealand, so if I'm buying any nice stuff from Sparkfun I have to pay lots for freight (Dammit) :-/