I've also got an I/O tablet (updated to 3.1) and I followed this tutorial, so thanks for the help you provided! I managed to copy some files to the device but it ended up freezing my computer (running Ubuntu 10.10).
So I unplugged the tablet, and saw that effectively those few pictures and pdf files had been copied to the device successfully. Pictures are in the Gallery, pdf can be read with Aldiko... but the funny thing is that when I mounted again the tablet -using Ubuntu again- it shows all folders as empty!
That is, 0 files in all tablet folders.
I tried "showing all hidden files" with Nautilus. No luck, nothing is shown. Went to the folder using command line, did an ls -la (just in case who knows! maybe it would show something!). No luck either, directories are apparently empty and have "1 January 1970" as modification date... if it helps.
I can see the files inside the folders using ADB but it's obviously not ideal, specially compared with simply using Nautilus.
Does it happen to you too?