It does vary from projector to projector. I've had 3, here are my experiences,
Mits HD1000U: Mainly just pumps up the whites, so you get an unbalanced image with overly bright highlights. No benefit IMO.
Infocus X10: Works better than the 1000U, but adds the odd pixelization in whites unless you reduce contrast quite a bit. Not worth it here either IMO.
Benq W6000: I'm actually using it with this one. Whites are ok and it does boost brightness across the board. In outdoor bright scenes I actually prefer it. Calibration still isn't as good though. In particular, light blue colors (think light blue sky, maybe water/ocean) are off and I can't find a way to fix them 100%.
I'm only using it with the W6000 because I have a large 1.0 gain screen and the extra brightness trumps the modest calibration problem (personal taste, some won't agree). Eventually I may get a higher gain screen and stop using it, although it does really look good in brighter scenes.