Thanks for your feedback, everyone!
Having looked more closely at our options, I think we are going to avoid the USB system if for no other reason than that the potential loss of data seems like a limitation. USB is not meant for constant writing of data, as far as we can tell, and this is exactly what we want.
So it seems we will be going with a Flash system. But which one?
We looked at the DosONChip sold by sparkfun here?
But in speaking to someone in the know and in doing research on this forum, it seems there are many unhappy costumers with this product. Its documentation is severely limited and more importantly, it has an upload transfer limit of around 480 bytes per second (see here: http://forum.sparkfun.com/viewtopic.php?t=5065).
It looks like after all is said and done, we are going to go with an Atmel AT45DB642D (http://atmel.com/dyn/products/product_card.asp?part_id=3777). It isn't removable, but it will provide us with around 8 megabytes of storage which will give us room to grow. Also, I called the manufacturer today and they confirmed this chip will write 1024 bytes in 17 milliseconds, plenty for our needs. Hopefully the library provided here will work, as both products are from the same family: Arduino Playground - Dataflash
Carlo and Don