balance

I'd like to start a discussion to collect general knowledge of what to do and what not to do when building a two-wheeled self-balancing robot (SBR for short).  My hope is that this thread can become a somewhat comprehensive set of guidelines to help beginners and non-beginners build their first balancing robot or  achieve a more stable and successful subsequent design.  Things that I would like to understand include:

Making a balancing robot - or even dreaming of making one just lost it's appeal.. because I will never make anything like this.,

I was just cleaning up my desk (a little anyway), and found myself sitting with the guts from a servo.

In essense I had:

A potmeter. If it was turned to one side, a motor would turn to one side, and vise versa. A little turning = a slow motor, hard turn = fast motor.

Hmm.. interesting..

Now, what if I was not turning this potmeter, but a simple spinning disc, acting like a simple gyroscope was attached to it?

Then if the whole thing was tilting in one direction, a motor.. OR a complete servo (with guts taken out) would turn to one direction.