I've been following your scalability proposal in the Technical Discussion section.  You want to see the max block size adjusted based on blockchain feedback (closed loop), whereas Gavin proposes an open-loop solution.  One risk with Gavin's solution is that it assumes historical growth rates for internet bandwidth will continue moving forward in time.  One risk with your proposal is that it introduces another feedback term into what is surely a nonlinear system (right now the only feedback term is Bitcoin's difficulty adjustment). 

By the way, has anyone heard from DeathAndTaxes?  I'd love to hear his view on both sidechains and scalability.