I only have my domain administrator account on a smart card to improve security in my domain, but this is not working as one can expect in Vista. Sometimes, especially when I wake the computer from sleep but also at other times, the credential tile for smart card authentication vanishes as the Smart card service stop working somehow. The only solution to this issue is to reboot the computer unfortunately. After becoming sick and tired of the problem I called Dell from which I got a beta driver. This driver seems to be somewhat more stable but not 100 percent stable. SP1 makes no difference either.