Check out: http://bits.blogs.nytimes.com/2013/08/2 ... t_20130829
In brief, massive study (630K transactions per week for many weeks involving 392 restaurants). By telling servers about the monitoring, revenue went up 7%/week (average of $3K) as workers channeled energy into upselling (and increasing tips) rather than theft, underselling, et al. All restaurants were studied before and after equipment was installed (and all employees notified).