USB drives are so prolific that they are now beginning to be given away free promotionally. There are literally thousands of different makes, models and capacities; all of which operate at different speeds. Of recent, the focus has been moving away from sheer storage to the speed at which you can fill the provided space, with people becoming ever more impatient.
With the 4GB barrier broken a long time ago, there have been more and more devices falling into this bracket of size. They are mostly the same and rarely have differentiating features, and most come with an encryption program to stop an opportunistic thief running off with your important documents.
Today I have the Lexar JD Secure II 4GB which has a nifty little feature that separates it from its other 4GB cousins.