Rhythmbox and gtkpod are currently able to fully read and write the iPod databases. However, though the iPad uses a very similar database, and is claimed to be supported by these applications (you can choose the xC497 model in the database setup), there are some problems stopping the writing to the library.
Upon any database interaction (loading the iPad, adding music or videos, deleting items) a warning appears: "Unsupported checksum type". The iPad says that it is syncing, but no changes take effect. I have noticed though, that the files are correctly manipulated in the filesystem: deleting an item makes it unplayable (as there is no file) but still listed in the database. Adding an item copies the file, but fails to add to the database.
After doing a bit of googling and code searching, I came across this thread:
http://ubuntuforums.org/showthread.php?t=1481799
>Will the iPad (using OS 3.2) work with libimobiledevice?
>Yes it will. We tested access and all tools work as expected. Changes are in GIT
>and support arrives in the next releases.
>
>So everything works?
>Not everything. The iPad uses a “DBVersion 5″ for it’s music database and apparently
>a new hash algorithm. However, we’re already looking into it and hope to have
>everything working before iPhone OS 4.0 arrives to keep people syncing fine.
This thread was a little while ago, but no further achievement has been made concerning the writing to the database.
Thank you for your bug report.
About writing to the database, it's a problem with libgpod. Support for iPad in libimobiledevice should already be available, but the support sync music database it's still missing in libgpod.