As a DBA I'd like to identify unused collections so that I can remove them to optimize performance.
As of now there doesn’t seem to be a direct way. One option could be to settup auditing or using logging (e.g. set the slow op timer to 0 so we log everything).
An other might be to use the collstats command and frequently traverse all collections..

I'd be happy to get a direct method to show me unused resp. last usage of a collection. Based on DB level or even over all DBs.