[[Stock <cough> (UK MZ604 version but converted to GED) ICS on build IML77. NOT rooted (yet).]]
Interesting. I can't create with Astro but installed File Manager HD and I can create a folder on the sd card, so that is a great tip. I can't delete it though :'(.
I have had no problems at all with writing using a USB lead though. I guess you have to have the correct connection settings switched on (Settings > Storage > Media device)