One thing that put me off Steam for a while, was it's noticed tendency
to 'break upon update' when being used not only in CXG, but a lot of
the time this sort of thing hits windows users as well....
...knowing this, I always do the same as Samuel...everything gets the
steam based backup dump (for a newly downloaded title) even before
I actually run the game at all - this covers two boundaries, 1 - you
never need download the data again, and 2 - you've got a 'pristine'
backup that's not ever been run and had any files futzed with that
usually occurs at first time startup (or a title)...
...in this sort of case, on linux, what I do is just leave everything
be in my -working- Steam bottle collection, and move the entire contents
of my ~/cxgames and ~/.cxgames to somewhere else, do a fresh CXG install
followed by a fresh Steam GUI install and try to work out 'what happened'.
The way I figure it, if a fresh install doesn't make the Steam GUI work,
there might not be an immediate workaround...
...I'm still trying to conclude exactly where what why went woopsie...
edit: oh...I forgot to say, I already have a workaround, but it's not
much use if you haven't prepared for it...ie; I have a cxarchive here
of a base Steam installation bottle of the client version that would've
been current back in 12/09 - this bottle, is set to offline mode so I
can call on it (restore the bottle) when stuff like this happens. Then,
don't let the thing update itself, restore desperately needed gaming
experience you can't live without...or even leave the thing in offline
mode until things are all better...