To be perfectly honest, flash drives are such simple devices that I haven't really noticed any difference in them. I've bought tons of flash drives from the most expensive to the cheapest pieces of crap I could find. I recently found 2gb flash drives for $5 at walmart, and they're surprisingly okay. Aside from the cheap ass plastic that kept peeling off, it works just as well as my $15 2gb flash drive I recently bought.

I've streamed video on it, used it with windows ready boost, copied its entire contents multiple times, and done pretty much my normal activity on it. I tend to believe that you pay for how cool the flash drive looks and how thick the plastic is, NOT how good the actual function of the drive is.
Of course this is just my personal opinion. Some other people feel differently and I respect that, but I just haven't personally experienced any real difference in them (and believe me, I've bought a lot of them).