Gnome hangs on startup - how to get more info?

[Simon Kitching <skitching apache org>]

Hi, 

I'm running Debian Sarge (gnome2.8) and recently apt-updated, and gnome
has broken. After logging in with gdm, I get the gnome spashscreen. A
few progress icons appear on the splashscreen, then everything hangs.
ctrl-alt-backspace returns me to gdm, where I *can* successfully log in
to KDE. 

Can anyone suggest where I might look for more diagnostic info on the
problem? I've checked ~/.xsession-errors, but there isn't anything
helpful there.

Thanks,

Simon