Eivind, currently we don't track the actual logins of a user. This would be a very useful feature though. This should be part of an audit log where all activity are logged. E.g. logins, edits, creations, removals.
We are accepting patches to eZ publish btw, hint hint ;)
That would be great Eivind, I know other users want this feature as well. It's also a nice feature which gives you overview of actions done in the system.
Looking forward to seeing a contribution from you ;)