It makes you wait for slow-to-start programs to show their stupid window to avoid them popping up when you do other stuff in the meantime.
Hell, GDM is even so ****ing stupid as to place the greeter window and panel on whichever monitor the cursor is currently on, including a "race condition" that allows the greeter to show up on one display and the panel to show up on another.
Then comes the fucked up resolution, that is totally not the sane value you chose in DisplayPreferences for your desktop.
Now this becomes really FUBAR when you decide to rotate one of your screens. GDM is of course not rotated, so you might end up with the greeter window on the rotated screen.
Why is it so hard to change settings for the gdm screen? Why not "apply for gdm screen" checkbox in Display Preferences aka gnome-display-properties (another fuck up, the naming).
There is no much small things to fix in gnome2 and they waste time on that (probably useless) gnome3 thing.
Oh, and just to top it off, the Linux r600 driver lists my displays in reverse order of Windows, so whenever I change OSes I need to swap cables to get the monitor that's actually in front of my face to be the primary display. Lovely.