Check what accounting options are available for your system.
In opensuse 12.2, I see that there is a package called "acct". The documentation says
acct - User-Specific Process Accounting
This package contains the programs necessary for user-specific process accounting: sa, accton, and lastcomm.
I'm pretty sure that is what you want.
I don't have it installed. I do remember using it on an earlier unix system (around 1990).
Note that it will provide information all all commands used, not just those started from the GUI.--
AT&T Uverse; Zyxel NBG334W router (behind the 2wire gateway); openSuSE 12.2; firefox 15.0