lsof | grep home/$USER and I found that the gmain process likes to open my personal files. What does this process do and is there any available documentation that explains it in context of Ubuntu?
All about gmain can be found on the gnome developer site. 1st bit of the description for it:
The main event loop manages all the available sources of events for GLib and GTK+ applications. These events can come from any number of different types of sources such as file descriptors (plain files, pipes or sockets) and timeouts. New types of event sources can also be added using g_source_attach().
Basically it handles anything gnome event related.