Go to this page on the demo server...
It doesn't show any users are logged in. You're logged in, so it should at least show you.
The same thing happens on my server running OpenMRS 1.10.1 (with OpenMRS 2.1 modules).
I suspect the problem is related to the OpenMRS 2.x user interface, but it could be a bug that was fixed in 1.11 already.