One thing that has been on my mind lately...how can folks reduce the amount of power that they are consuming in the datacenter. Very few architects look at power efficiency as a first-class system quality.
In my mind, this is something that is going to take a while to solve. It is roughly analogous to security as a system quality. Infrastructure architects can build firewalls, set up traffic monitors, but at the application layer architects have to consider security important and architect their solutions with that quality in mind. It's the precise same problem with power. We will see initial stabs from the infrastructure side of the house, but it will be a while before apps are power aware.
I think that green is the next big thing in the datacenter, and not just because of environmental concerns. Power is expensive and getting more so. Power cost quickly dwarfs acquisition cost. Architects need to consider these things when they design systems.