The wispy (or the USB layer) is unstable - I'm using it in OTG mode and I have it plugged in before I startup spectool, but it still sometimes locks up.

You can try the flash drives in a powered hub. I've had success and failure with different drives - my belkin (which also works with the ipod camera connection) works with a CF, but I have a $5 SD reader which won't.

But a microSD flash drive (DealExtreme.com has them) works fine and I usually use it to transfer files instead of using the longer nokia cable.

Also note that the autoswitch for OTG may be more (or less) reliable with a particular drive or device. I'm generally using the modified micro to mini adapter.