Powerstrip is a very powerful program that allows you to do an assortment of stuff including color correction, level adjustments over screen geometry, driver independent clock controls, it can detect what program you are running and respond by activating specific display settings for those programs, and a whole lot more. I pretty much just use it for cutom resolutions and and refresh rates.
Powerstrip is not an easy program to use, it’s not hard either, but it takes some knowledge of what you are doing to do things correctly. The people over at the AVS forums are a great source of knowledge if you ever have any questions regarding powerstrip.
As I stated earlier, the main reason that I am using powerstrip is so that I can run at a custom resolution and refresh rate. Video card manufacturers are getting much better about suppporting widescreen resolutions with their drivers these days, but when I put my HTPC together I needed powerstrip to get the custom resolution that I wanted. I am running everything at 1280X720 at a refresh rate of 71.928Hz. Setting up powerstrip is much more complicated on a rear projection TV due to overscan issues on many rear projection TVs, this is something I will not get into here (since I know very little on the subject).
There is already a good write up on configuring powerstrip so I wont really get into it here (The link is at the bottom of the page). But just make sure you do your homework first and take things slowly and you will be good to go.