http://healthland.time.com/2011/04/13/the-dangers-of-sitting... http://vuir.vu.edu.au/21403/1/Van_Uffelen_Occupational_sitti...
Like everything in life, moderation is the key. If you are getting up and down from your desk regularly anyway then the health benefits wouldn't be very large. Standing all day isn't particularly good for you either.
I believe the science is still out on this. My main issue with the current studies is that the occupations are different. For instance, what is the difference in stress between a GP and an accountant? As far as I'm aware, there haven't been any studies that compare mortality that control for the 'same occupation'. The studies thus-far have only shown that people who have occupations that require standing tend to have lower all-cause mortality than those whose occupations usually involve sitting. If there is such a study then I’m interested in reading it.