Sharing is pretty awesome... unless you're 3.
I hated sharing as a child - which shouldn't be surprising because I'm sure all children did. Especially when I had to share with my younger brother. I was here first, and those toys were mine first...
Now that I'm a little older, sharing is completely different. Yes, I draw the lines with a few things (chocolate covered marshmallows for one), but 99% of the time I'm an awesome share-er. Sharing, whether its through sharing things, facts, knowledge, or whatever, sharing helps deepen a relationship and allows for connections that may not otherwise exist.
But I still won't share my chocolate covered marshmallow eggs with you. That's where the line is drawn.