Drawing on some good work from mumsoft, I've found a way of copying my music off the Olive on a Windows computer - complete with metadata and with separate folders for the different CDs.
I thought I would post it here, so it's available to everyone.
First, I made a backup on a portable harddrive. (This was made using Olive's old firmware, but I assume it will still work with the new firmware).
Second, I connected the harddrive to my pc and copied the files. As the Olive uses Linux, it is is necessary to mount the drive using special software. I used DiscInternals Linux Reader (which is freeware). Google for discinternals. The main files containing the music are a series of 2GB files named audiolibrarybackup.taraa, audiolibrarybackup.tarab etc. I copied all the files onto my hard disc - I had to copy them in batches of 40 files or so, as the software was very slow 'enumerating the files' (as it described it). These files, when combined, are one large zip archive.
Third, I concatenated all the files together. (I found opening audiolibrarybackup.taraa only opened the music in this file - not the others. I think Mumsoft, who was using Linux, didn't need to do this - but I could be wrong)
To do this, you go to the command line prompt (type cmd.exe in the search box), then navigate to the correct directory. (cd is the change directory command; the drive letter followed by colon changes drive. So type d: then return, then cd \\music\\olive to navigate to drive d and a subdirectory olive in a directory music)
You then type the command copy /y /b audiolibrarybackup.tar* combined.tar
This combines all the files into one single file called combined.tar. This will take some time.
Finally, you use 7-zip to open and extract all the files from combined.tar.
I've been using compressed flac. In my case, the files were contained in separate folders for each cd (except the files which had been copied from my computer - which were in an imported folder). The flac files contained both the metadata and artwork when opened in Mediamonkey.
All of this takes a while and a lot of hard disc space (as you wind up with 3 copies of your music). You can delete the original files after combining them if this is a problem.
No warranties given, but hopefully this will work for everyone. Obviously, this only applies to Windows computer - but I suspect you could adapt this to a Mac.