I have thought of this subject too. As I am interested in Digital Audio Processing for musical instruments and PA systems, I have wanted to design reverb/delay units that use SDRAM modules. Firstly because of the price. Here in Australia a 256MB SDRAM module is currently around AUD$80 - for 256MB RAM!. But if I wanted 2MB from discrete DRAM chips it would cost just as much. Secondly, in mobile equipment it is always best to limit or remove any moving/mechanical parts. No need to explain why. And Hard Disks are too slow. The cost of Flash cards/modules is off the scale on the outragous meter. All this leave SDRAM as the only choice (what a wonderful language the English one is - the only choice HA!)