>> Does "stationary" actually mean anything in absolute terms?
>
> That's kind of my point.

Actually for rotation, you should be able to define stationary.  Because in 
order to rotate you need some force to stop you flying off in a straight 
line.  On the surface of the Earth, the downwards force that you feel is 
ever so slightly less than what it should be due to gravity, because the 
Earth is rotating.  If the Earth rotated at the right speed then there would 
essentially be no downwards force (at least on the equator) and everything 
would float.

So, assuming you can measure forces and calculate gravity accurately enough, 
you should be able to determine if you are rotating or not, and how fast you 
are rotating.

Another method might be to use a gyroscope, it will react differently if the 
planet you are on is rotating or not.

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