Creativity comes out of the woodwork!
I love watching how Google+ gets 20m users, and does not yet have an API, but because of Chrome, and Firefox + other clever techniques, developers around the world come out of the woodwork, stay up late at night, and create new plug-ins and innovation to enhance Google+. And it just takes days, and in a few weeks, there are some fantastic products.
This list below is by no means complete, but shows a few.
What features do you need the that these do not deliver?