Mass workload monitoring?

[yegorm]

Hello,
In our customer's system there are sometimes a lot of workitems
accumulating in users' inboxes. It typically happens to users who are
inactive or absent and so on. As a measure against this situation, we
are looking for some way of mass workload monitoring. Something
similar to SWI5, but giving statistical overview instead of one
particular user's detail data; that could list users whose number of
workitems in inbox has exceeded N.

I didn't find any standard reports to provide these data. Could you
recommend any?

Thank you in advance!