We had a chance to see Patriot's 32 and 64GB USB keys. Even 32GB sounded crazy to us, and we had a chance to test one shortly before Xmas; but seeing that the company is currently almost ready for 64GB this will give you a glimpse into the future.
The technology is there, but 64GB USB would be too expensive today. It should be ready by the end of this quarter or very early in Q2. It looks identical to the 32GB version and differs only by the 64 numbers on the case.
At the same time, 64GB will show the same speeds as 32GB.