FPGA newbie here; How does this relate to toolsets that Cadence, Synopsys and Mentor Graphics and others make for chip design? Would you use tools from these companies to design VHDL / Verilog for the 'FPGAs as a service' or is this at all related?
Those tools are very close to silicium level design tools.
I guess the smartest application of FPGAs on EC2 would be for FPGA design tools, they are incredibly slow.