I use Dropbox to transfer file (ebooks, documents, images...) to and from an iPad and 2 ubuntu laptops in the same LAN, but it's a nonsense to move files to the cloud and back again to the same LAN.
Is there a local alternative, such as setting up a samba share, or a ssh/scp/sshfs service, or rsync on the ubuntu pcs, and accessing it via some app on the iPad?