I did some more digging and found info on Desired Gamma here (a page from Yves' website using the Wayback Machine). The paragraphs that apply are these:
This would mean that the "Current Gamma" should be set to the gamma of your monitor (which should be 2.2 for everyone). Then, the "Desired Gamma" is set to the gamma correction planned...which, if rendering to a 1.0 gamma OpenEXR, needs to be 1/2.2 according to this illustration (found on this page):
Reading Yves' description, I would assume this correction for a 1.0 gamma would be applied when "Desired Gamma" is set to 1.0, but that doesn't work for me...I get a white screen. It does appear to work if I set the "Desired Gamma" to 3.4. I've been using 3.3, but if it's supposed to work at 1.0 there would be a difference of 1.2 and that would be 3.4 (going in the opposite direction). So, I'm thinking that "Desired Gamma" may be working, but in the opposite direction as intended? Well, as long as it works.