Lyx supports document revision control for collaborative document editing. It uses rcs, a gnu revision control system, for that purpose. You and your colleges then can register, checkout, merge and commit into your shared documents.
In Ubuntu Lucid, It was not installed by default when you installed Lyx package. So, you have to install rcs package using apt to enable Lyx revision control.
$> sudo aptitude install rcs
That’s it. You now can use revision control feature for your document. It is found at Lyx File menu.
First, register your document and than checkout it for editing.