tracing user actions

[<bhugueney altern org>]

Hi,
I'm soon to be involved in user-computer interactions studies.
We will need to collect usage data to analyze how students are using a software environement.
I would like to be able to use the gnome software, but I would need to be able to log *every* user interaction with applications. Not on the X events side, but on the applications side. 
I thought that libs could be hacked so that upon processing a gnome (gtk?) event, the processing object could write some logging information.
I have zero gnome-gtk knowledge for now, and would like to know if this would be possible at the gnome level, or if I have to used an environement OO toolkit. (No flame intended but GUI elements could be inheriting from an EventObserver class with a virtual member logging function querying for the precise GUI element)

I've been searching for "tracing" and "logging" on the mailing lists archives, but to no avail ...
GtkTrace might have been useful, but it disapeared.

I am willing to code, and think that both code and results of the study could be very useful to Gnome.
But of course I would like to write the minimum code (that's why I'm lloking for a per-library approach instead of a per application approach), and I would also like to avoid rewriting something already available.

Any ideas ?

Thank you very much in advance.

Bernard