You should have done some quick benchmarks before you installed ReadyBoost. Measure boot-up and shutdown times, file transfer, etc.

My experiences with ReadyBoost and SuperFetch enabled on a 2GB laptop with a 2GB SD card used is noticeable but minimal.

Um, no. I use a stopwatch ;) as it's not that big a deal to me. I'm sure others will know more though.
Maybe whs' abacus or Lighthouse's divine intervention may be better tools.

Look into the USB drive Properties > Readyboost once. There you see how much space was allocated for the readyboost. I bet it is less than 1GB. You will also notice it when you reboot your system. It's slower to come up. I found that readyboost does not really help, especially if you use very different applications all the time (changing POR = point of reference). Vista writes to both, the disk and USB (because it has to be safe in case you pull the USB) and for read it checks the USB first and if not found it goes to disk. All of that is overhead. I have never measured the difference, but logic tells me that it cannot be that great. I also noticed that it made the system more instable.

@Scott. Stopwatch? That's a bit high tec!