I regularly have applications which restrict access to a single logon, on a single PC, with the same user name. To achieve this all users have to logout properly, so that they clear down a unique logon GUID is the system database. Being human, not all of them click on LOGOUT within the application; instead they just close the browser directly. When they next try to logon they are warned someone is already logged on with the same user name and have to confirm that they should log the other user out. ......
Going to DDD 2 on 22 October in the UK?
If yes the get voting here, http://www.developerday.co.uk/ddd/votesessions.asp, on the sessions that you wish to attend.
It looks like a really great range of topics are being covered so there is definitely something for everyone in there.