Thank you for your feedback.
Sitefinity constantly undergoes performance improvements, and we are aware of some unresolved issues which are still pending. Pages which require authentication would most probably initiate a user query upon their request, but at some points there are, indeed, calls which may be reduced.
It would be quite helpful for us if you could supply additional information about your system status, Sitefinity build, and the scenario you normally run, where exactly you've encountered this, and if you could specify in greater detail what "every second" actually mean?
the Telerik team