I have the Ikea Markus at home and it's been fine, especially for a $200 chair. I use a Herman-Miller Aeron in my work office that I got when I was having back problems, and like it a lot ... but I've found the Markus to be a good solution given the cost disparity. I don't feel like I need to spend $1000 for my home office.

Seconded.

I could have sit on it for 15 hours a day without problems. Other types of chairs caused back pain after only several hours.

I prefer the Ikea Malkolm which is also a tad cheaper.