I've had a chance to play with one of the new Iomega ZIP Ultra 750 and I have to admit is that it is a pretty nice drive. In certain cases it is more convinient than regular CD-RW, since there is no software needed just to get basic operation of the drive. ZIP disks also can be protected by password, while CDs can't.
As far as compatibility, 100MB ZIP disks are supported only in read-only format, while 250MB and 750MB are in read-write mode.
Iomega ZIP Ultra will come in two flavors, USB 2.0 (compatible with USB 1.x as well) and Firewire. Both will require an external power supply.