So I did about a 300 mile ride and noticed that my oil pressure light was starting to come on at idle.  Because i'm I like gauges of all kinds, I also have an oil pressure gauge hooked to it.  At idle I put out about 20 psi.  At speed it's about 60.  These figures are at operating temp and have not changed since I installed the gauge about 6 years ago.  I'm thinking the sending unit is done.  Any one know at what pressure the light should come on at?

The sending unit, is known for leaking, and some failures. If the idle is low it will come on, and I've heard of it if it's been really hot.

I wouldn't worry too much about it, seeing you checked the pressure already and the light goes out with throttle.

It is only a $30 part, replaced mine for leaking once.

   I can't remember where, but i read somewhere that the sensor is set for 16 psi.
I recently had the same issue and also installed a mechanical guage. When hot it holds 20 psi at idle and 65 psi at anything above.
  I've also been told, by reliable sources, that the engine can operate normally with as little as 5 psi.

Assuming your pressure gauge is good, the sending unit is toast.

1.1 Bar minimum cold, 4 Bar minimum hot.