I started working with Lightroom since Lightroom 2 came out and have never looked back. It is a program I really love to use. I think it is perfect for photographers and each version that comes out just keeps getting better. This latest release of Lightroom is no let down for sure. I really like the added adjustment brushes and also the soft proofing ability right in Lightroom!
Below I have posted a before, after and final version of a portrait I did of a local chef. I edited them all with Lightroom. When I shot this image, I exposed for the background and strobed the chef with an off camera flash. I then did my normal adjustments in Lightroom 3. The before is the result. To take it one step further I adjusted the After image in Lightroom 4 using the local adjustment brush. I adjusted the white balance on the chef and his jacket. I did his jacket just to show the difference you can make with changing the white balance in a specific part of a scene. In the final version, I only adjusted his face and arms. The jacket I just reduced the brightness a little and that was it. The light on his face was a bit whitish from the flash and kind of harsh but with the adjustment brush I was able to ajust the white balance to more of what the abmient light was on the scene.
You can go to http://tv.adobe.com/product/lightroom/?trackingid=JPKPN to watch video tutorials on LR. Have fun!