I keep mine right at 25%, if you don't use your phone that much you could easily get away with 50%.

 

I keep mine about 1/3. Seems to work well in almost all lighting.

 

Almost always at 50% unless I'm outside. There is virtually no difference between 50% and 100%

 

25% for me.

 

About 20%, sometimes less. I work indoors in a VERY dark environment so minimal lighting is more than enough.

 

20 - 25% for me

 

When I was running Android 1.5 on my Sprint HTC Hero I had it set to the automatic brightness setting. After I updated my handset to Android 2.1 I had forgotten for a couple of months to set it back to automatic brightness. It was on automatic brightness by default in Android 1.5, so I am not sure why they changed it for Android 2.1. Anyway, a couple of weeks ago I set it back to automatic brightness.

I noticed a fairly nice bump in battery life after doing so. I mean, my battery life was already quite good with Android 2.1, but I was not going to complain about even more battery life.

 

I keep mine 0% indoors with 10% being the highest indoors.

outside in the sun I keep it at 25%min, if it's very sunny I'll do 50%.

 

I just leave mine on Auto. Seems to work just fine for me.