Every pilot should definitely read these two articles:

Review of Nonin Onyx Pulse Oximeter
(has good info that would probably apply to all brands of oximeters)
http://www.aeromedix.com/aeromedix/art/pulseox/

Respiration: What Pilots Need to Know (But Aren't Taught)
http://www.aeromedix.com/aeromedix/a.../respirat.html