@mp5gosu: peter guthrie and berntrand are changing gamma (or is it gain?) for quite some time now, based on their blog reports. So i the rest of the community. So I don't see anything wrong with it, results are great and so is the workflow (no need of positioning the sun to fir the HDR). But I wouldn't change anything besides gamma(gain) though!
As soon as you start adjusting HDR Gamma, you are manipulating the way they HDR lighting is cast. Let's assume an optimal, perfectly ranged HDR, with overcast sky. When using this as GI Source, you will get soft shadows. Now if you want hard shadows and you're using HDR Gamma, here are 2 points to consider: Overcast sky never creates sharp shadows. (To that point, you never want to deal with HDR gamma, but replace the HDRI with one where the sun is visible to achieve sharp shadows).
Secondly, if you decide to create sharp shadows adjusting the HDR Gamma, you have to keep in mind, that you do a curve manipulation which lead to results that highly differ from what it should be and what looks good. (I.e. crunching midtones, killing dark areas, etc.)
Btw: Good HDRIs always have linear color space and should be treatened like that.
But I have to admit, if you're using really low quality (low range or LDR) HDRIs, HDR gamma could make sense and helps to improve your image.
But in general, you should stick to high quality HDRIs, probably buy some good ones. Then you will not run into any shadow and accuracy issues most likely.
Oh and by the way: It's not entirely wrong. It's still up to the artist, to gain a decent style of lighting. Boosting shadows and bright areas can be done with gamma, but can also be done in post, with FULL flexibility.