Quote - Assuming you're using PP2010 with GC enabled:

• incoming colour maps are automatically linearised so they play nicely with the linear maths in the shader nodes
• when you save your render a gamma curve of 2.2 is applied because that's how digital images have to be encoded
• unless, that is, you save your render in HDR or EXR format: these are (I think) 32-bits per colour and remain linear (i.e. no gamma curves are applied)
• this means you have full control over gamma, and lots of other things, in Photoshop and if you use the 'Exposure' adjustment layer it is non-destructive

The best analogy I can think of is when using a digital camera: you have the no-brainer option of shooting to JPEG or the far more flexible option of shooting RAW images. 

 

You will also find you need a lot less light than you needed before. This has a knock-on effect since anything which is self-illuminated becomes too bright.

I recommend trying a test render with all lights off. This will show you what has non-zero ambient, translucent, alternate diffuse, or alternate specular. You can either zero these (or disconnect them), or rework the shader tree. (I'm fond of multiplying the alternate specular or alternate diffuse input with a diffuse node, so that it only has that effect where there is light falling on the surface.)