This is probably the neatest web framework of any language I've used. The only downside I can see is that it stores the app states in sessions in the form of c

This is probably the neatest web framework of any language I've used. The only downside I can see is that it stores the app states in sessions in the form of closures, and since you can't easily serialize closures, each session is stuck on one machine. So if you want to scale to multiple machines, each user will have to use a single machine for the entirety of the session, which could result in load imbalance with traffic-heavy sites. This is only in theory, it would be nice to hear some stories where sticky-session has not been a problem in scaling.