WES is Wireless Enterprise Symposium. It is a 3 day conference put on by RIM for BB admins, CEOs and such to learn more about BB and all BB related vendors are in one place. There is also formal training that happens as well as hands on labs so people can play with BES without messing up their own installations.
It has some good evening events as well and the networking with other BB admins throughout the event has proven very invaluable to me. This will be 7th WES and it is a good event.