In a Nutshell, The Difference between an Event and a Delegate

An event simply adds a layer of protection over a delegate instance.

This protection prevents clients of the delegate from resetting the delegate and its invocation list, and only allows adding or removing targets from the invocation list.

Source: http://weblogs.asp.net/rosherove/archive/2004/03/28/100444.aspx

An esteemed colleague directed me to a post (can't recall) that further elaborates on the distinction. The main one that I remember is that in addition to the = restriction, invocations of an Event are restricted to the class that owns the event.

So if you want to allow other classes to raise an event you must expose a public method to that delegates the raising.