What would be really interesting is if they thought of a Hybrid-Cloud approach. I recall Joel talking about adding a new server every week due to Trello's ever growing popularity during his presentation at Startup School. Being able to spool up on-demand should really help with performance or for times when the datacenter is flooded. But wouldn't it be more cost effective to run it on your hardware during off-peak times and spool up some new servers on AWS when performance starts to lag?

Disclaimer: I'm a Trello fanboy, it's like having container classes in STL, only more visual!