At some point, I'm going to guess that even moderately large AWS configurations would be better off getting a high capacity business FiOS line (or whatever the next tier is), get a couple racks full of home rolled high-end systems and staff 2 or 3 guys full time to run everything. The systems will be faster, probably about as reliable, everything will be cheaper even with extra people on payroll. I'd love to see some…
Sure AWS is expensive for 24/7/365 applications, but I suspect there's some "in between ground" where Amazon's economies of scale make it less expensive to just pay them to deal with owning and maintaining the hardware (and ensuring you write your applications to be able to deal with cloud instances vanishing underneath you randomly).