Kingston launched a USB key offering 256 GB of storage space: DataTraveler 310.
Based on USB 2.0 format, you will need time and to be patient to fill it up as it writes data at 12 MB/s and read them at 25 MB/s. In other words, it will take you about 6 hours to saturate the storage space, while it will offer you about 3 hours of reading from it. It seems quite clear that for such large portable storage unit, the USB 3.0 format will become the default system.