i have an a5000.

gotchas about them:

-you can put any sized hard disk, but you can only partition up to 8 gigs. still, i've got a 4.5 gig disk in mine and it is nowhere near full.
-hard disk access is slow - a 60 meg library takes 2 or 3 minutes to load.
-not too many commercial sample cds available (but they will of course play regular wav files if you use cdxtract or something like that to get the samples of an akai disk...)

but there are a lot of good things about them. 32 midi channels, 129 voices of polyphony, lots of eq and filters and lfos for sound shaping, and the fx are half decent.

despite the fact that it only runs at 16 bit, the converters are pretty good. i sampled a tb303 straight in and playing the two side by side, you couldn't tell the difference.