If I remember correctly, no. To save samples & sequences you gotta go smart media card or scsi hard drive or burner. Even if you can use the USB port to run to a usb zip drive, to say transfers would be hella slow is an understatement.
What you can surely & reasonably use usb for is to communicate with your computer - think sequencing with software vs. the Motif's internal sequencer.
Check your manual, it's all in there (well most shit is).
Check here, too:
http:www.motifator.com
and read all info you can stand in the "Behind The Manual," particularly the power user docs on sampling, resampling, etc...
and if you just gotta have pads to bang on with your fingers, Spin's advice is dead-up perfect re: the MPD 16. Native Instruments' Battery is optional...