Diff? on Flash speed in running PAs?

Go with the fastest you can afford. It makes a big difference on how responsive your portable apps will be. You want something with at least 20 write speed. Mine has 25-30 and it's fast enough that I don't have to worry about tweaking apps to limit writes. Reads are generally not a problem if the drive has fast write speeds.

Sometimes the 8GB flash models cost about as much as mechanical drives of much higher capacity, which might have better performance too. Depends on what you are trying to achieve. Flash might be less susceptible to mechanical problems (dropping) but is definitely susceptible to failure after a relatively low number of writes (>10,000 but still relatively low).

Definitely get the best you can afford, using your own definition of best. You may care more about performance than security, for example, whereas someone else would be willing to sacrifice a bit of performance for a better password protection scheme.

The software that comes with removable drives is optional. You could copy it off to a CD or something in case you want to play with it later. But it also (in it's pre-installed form) uses relatively little space.

I thought Readyboost was configurable -- doesn't it only uses the storage you designate for it? The space you configure is no longer available, but that's your choice. The other thing about ReadyBoost is that drives have to have pretty decent performance to carry that label. Maybe someone here knows if "Readyboost capable" drives sacrifice anything if they aren't configured or used for Readyboost?