Q: User quits unexpectedly

What you're describing is probably a WindowServer crash. Look in /Library/Logs/CrashReporter and ~/Library/Logs/CrashReporter for the latest crash logs. Also look in system.log for error messages preceding the crash.

If you can reproduce the crash by taking a certain action, such as waking from sleep, that will make it much easier to track down.

Uninstall the Trusteer Rapport product, and never install such garbage again. Follow the vendor's instructions to remove it -- I can't tell you how. After uninstalling, boot in safe mode (shift key down at startup) to rebuild your caches, then reboot as usual (i.e., not in safe mode.)

Yes. There's still something in /Library/Rapport. I can't tell you whether there's more somewhere else. If you post a link to the installer, I'll look at it.

This is an utility suggested by my canadian bank.

That's because your bank has a lazy, incompetent IT department. Instead of educating users on how to avoid phishing sites, they tell you to install a rootkit. You need to understand something here: the Trusteer product is a rootkit. When you install a rootkit, you're giving up control of your computer and your data to strangers whom you have no reason to trust. They can then do whatever they want.

If this is crap, many will or are having problems.

Many are having problems. Do a web search for "trusteer rapport crash." Very few of those installations are on Macs, by the way.

Anyway ... this is the link to the Uninstall web page

You need to delete all the following if not already done, then reboot twice as described above:

/Library/LaunchAgents/com.trusteer.rapport.rapportd.plist

/Library/LaunchDaemons/com.trusteer.rooks.rooksd.plist

/Library/PreferencePanes/RapportPreferences.prefPane

/Library/Rapport

Were the WindowServer crashes related to Rapport or did we only do this because you knew that it could cause some problem ?

The Rapport shared library was the only extraneous involved in the crash, so I think it was the cause.

Is there anything else I should do or that you saw in the crash logs ?

Not if you don't have any more crashes.