My experience has generally been positive with standing desks. I have the 'IKEA' solution at home and in the winter months I turn my work desk into a standing desk. This helps keep my core and back strong enough for biking in the constructions months.
But I can't do it for eight hours, I usually end up sitting on a tall stool at the end of the day.
Remember that a lot of people HAVE to stand all day at work and have a myriad of problems from doing so. Damaged knees and joints are probably at the top of the list of problems you might incur. Make sure you have a gel standing mat, good shoes, and a way to turn your desk back into a sitting desk quickly or a tall stool.