The solution to all of eye strain, hand strain, and ass strain is simply to take five minutes to leisurely walk around the block once every hour and half. You don't need an expensive chair or to work standing up or anything silly like that. You don't even need a daily exercise regimen.
I find the claims that people sitting all day is a new problem somewhat dubious. People have worked sitting down all day for centuries. I'm pretty sure what's new is fat people who never walk anywhere.
I second the recommendation of Workrave. It's easily configurable and it works quite well to remind one to get p every now and then (or at least to look away from the monitor for a few seconds).
Just because people have been sitting/squatting whilst working in previous centuries doesn't mean they didn't have problems. Have you seen the state of some poor people who spend their lives sitting badly whilst working?
I certainly get problems by sitting too long whilst working and I am by no measure fat. :) But, yes, get up and move about.
I find the claims that people sitting all day is a new problem somewhat dubious. People have worked sitting down all day for centuries. I'm pretty sure what's new is fat people who never walk anywhere.