This finally annoyed me enough to find a solution.
If I set a title on a gnome-terminal tab, then it gets forgotten next time I log in. Aside from the GNOME default to not save your session (whuh?), the problem is this: on Fedora, /etc/bashrc forces PROMPT_COMMAND to set the xterm title.
This wouldn't really be a problem, if I could disable setting of dynamic titles in gnome-terminal preferences. However, gnome-terminal thinks that a manually-set (Terminal->Set Title) title is somehow "dynamic", so if you do that, you can never set the title to anything else.
Seeing as I use the tab titles to work what machine I'm on, that's quite annoying.
The "solution" was to just edit /etc/bashrc so it doesn't force a PROMPT_COMMAND I don't want.