Comment 14 for bug 325051

It seems that (at least for Lucid) Gwibber is split in at least two packages:
- gwibber: the GTK+ gui
- gwibber-service: the application backend

Starting gwibber-service seems to do what you're looking for, so you can add to start at login.

This means that what's really wrong is that the gwibber preverences window provides an option named "start service at login". This is confusing. I propose this be changed to two (mutually exclusive) options:
1) Start gwibber minimized at login (adding gwibber-service to start at login)
2) Open gwibber at login (adding gwibber to start at login)