Use as a hard-disc? what? I don't know why they even bothered with this feature. When I want a disc I want it to:
1) use it wherever I want and don't have to care about admin rights or whatever - MDs (and iPod) -> no way I'm sure you will have to be root or something to install necessary drivers and simpleburner
2) transfering serious files - I currently use 20GB usb1 disc and the usb1 is slow as win95 on 386. You think that I want more than 12 Mb/s? Well I do atually, but the point is that with usb1 you can't get that speed. 12 Mb/s translates to 1.5MB/s exactly, but transfer rates for my disc are more like 0.6-1 MB/s (depending on number of files) and i guess MDs won't do faster. And believe when you are trying to move 500megs it's so so but for larger files you'd better be very patient.
At first I was very excited about HiMDs but now I think I will stick to my current gear.