Amazed this hasn't be brought up yet, so I'll do the honors:
If contracts can copy themselves, can self-modify, and communicate with each other, then it appears theoretically possible to envisage a model by which they could 'evolve' (similar to some of the theories advanced by Kevin Warwick for example).
Furthermore, this seems to clear the path for emergent behaviors.
What do you think are the limits? The geek in me quite likes the idea of the emergence of a collective intelligence (http://en.wikipedia.org/wiki/Collective_intelligence)
, especially as we're already talking about integrating sensor data via data feeds, internet of things, etc.