Dealing with Posture Problems?

WebfishUK asks: "Musculo-skeletal problems (such as back pain) affect most computer users sooner or later. Like others I spend many hours sat in front of a computer and wonder what the long-term health implications will be. I recently came across a website for an application called Posture Minder which apparently runs in the background and uses your web-cam to monitor how you are sitting and warn you about bad posture habits. It sounds like a neat idea (prevention being the best cure and all that), although the website doesn't have a download. Do Slashdot readers have other devices or any habits that they have adopted to mitigate the health risks of spending a lot of time in front of a computer?"