[PKSon]

When I first started getting into photography a bit more seriously, I asked a veteran enthusiast, "what's with the hood? Do I need to buy one? Do I get a rubber hood, or a plastic hood?"
This is what he said : "Don't buy a rubber hood"
He later elaborated for me..

hood's function : to prevent glare (ghosting)
SO, actually not used much. In the rare case where glare can be a problem, good. Otherwise, not much going on. Rubber? Of course not, hoods although normally not very useful, can protect your lens.

That's why I didn't use my hood that much. (Well, sometimes when I think I might need it for one of the two functions the hood has shown me)

I thought people having their hoods on backwards was cool, so I did that for a while, and wow, when I dropped my D300 with my 18-200 VR, everything just crashed. My heart stopped. I picked it up gingerly, and found that the BW filter was shattered, but everything else was totally fine. The hood had taken the first impact, thus saving my equipment.

When I use my Sigma 30mm in bars and stuff, I get a lot of ghosting/flares. So I put on my hood, and it's so much better when I do.

So in my conclusion, hoods - prevents flare, and protects the lens.

Oh, btw, IF, just IF hoods altered exposure in any way, then the lens companies are making it wrong. Hoods are supposed to be out of the angle/line of sight. Wider lenses have wider hoods, tele lenses have narrower hoods. No matter how much you zoom out, you will NEVER see the hood in the photo.

take care
PK