You guys beat me to the post about serial vs. parallel interfacing on high data rate A/D's. I've never had to work with really high data rate converters, but this always seemed to me like the biggest challenge. You're generating 10's or 100's of MB or more, continuously, in real time. That's dedicated discrete hardware at least, or perhaps an FPGA. Then if the data stream is truly continuous you have to dual-port the memory, or multi-bank it, or something. Sounds like a fun challenge but definitely a non-trivial one.