I'm doing this but I've found that having my feet suspended or only on the foot rest can lead to joint pain. I've set up a bench for my feet under the desk as a temporary solution but may spring for one of these ikea things and a nice chair in the future.

Also as a fairly active person (I run, ski, hike, bike, do yoga and climb pretty regularly) with aging joints I've found I need true rest/recovery time enough that standing the majority of the time doesn't work well for me.