There is currently no way (obvious to me at least) to see activity per user level. From a security perspective I'd like to be able to lock out users on an activity basis; ie you have to login with the account every 3 months or you'll be locked out. I'd also like to be able to set an expiration date on an account on which the account gets locked out.
Part of this maybe will be fulfilled by an audit trail covered by other posts but if not; it would be very nice to see when an account was logged in the last time. Would help a lot in keeping the user section clean.
We have actually recently added Last Activity and Last Login to the Users table. And the Journaling feature is soon ready for the public so hopefully that will fulfill your needs.