Actually, prices have come down. See here:

http://www.transintl.com/store/category.cf...uestTimeOut=500

It's still much higher than regular DDR RAM though. You CAN utilize more than bank 1 and 2 but the main speed boost is by running in quad channel (i.e. with bank 1 and 2 filled).

This of course depends on how memory intensive your work is. If you run quad channel with 2 gigs (512Mb x 4) and you hit a memory bottleneck; you'd still have a speed boost when you add more memory to the remaining banks, the speed gain however will not be as dramatic as going to quad-channel.