Here’s a cool little tip that’s actually been around in Lightroom for a while now, but it makes MUCH more sense with the renamed sliders in Lightroom 4. Basically, I get asked what the whites and blacks sliders are for a lot. I use them to set the white and black point in the photo. Usually, you’d think you have to turn on the highlight and shadow clipping warnings (by pressing J) to use them but there’s another trick. Next time, try just holding down the Option key (PC: Alt key) when moving the sliders. For Whites, everything will turn black as you drag it to the right. When you start to see some details popping up (don’t worry too much about the color) that means you’ve got a good white point.
(here’s an example of what you’ll see – click to see it larger)

Then drag the black slider and everything will turn white. When you start to see a decent amount of black specs showing up, then you’ve got your black point. Setting a white and black point have been around for a while in Photoshop, so it’s definitely nice to see them show up in a more consistent way in Lightroom. Enjoy and have a great weekend!