Are there any plans to include a system in Longhorn to limit and/or log the number of user logons?

No. Given the AD architecture, such a feature would not be easy to implement beyond a single domain controller environment.

Thomas Lee wrote:No. Given the AD architecture, such a feature would not be easy to implement beyond a single domain controller environment. Why would that be? There are already tools to examine the local logon caches of each DC to find out where users have authenticated and code already exists to quickly forward password changes to the PDC FSMO so I don't see why this couldn't be extended to logons.

This has been a feature often asked for - and it's never been implemented. To do for one of two servers is easy, but what about for a global enterprise. AD is not designed for this sort of operation.