User Profile Service
Windows Vista Service Details
User management. If disabled, prepare for some fun times getting it set up. It tries to look for your desktop in the system32 directory, loses all your start menu settings, and Services won't run. I won't guarentee this will happen to you. Just reboot into safe mode if you get in to trouble.
Responsible for loading and unloading user profiles. If this service is stopped or disabled, users will no longer be able to successfully log on or log off, applications may have problems getting to users' data, and components registered to receive profile event notifications will not receive them.
Consequences of Stopping:
All services listed in 'Required For' will be unable to function