Passing on some hard-won knowledge here:
Since upgrading to version 4.8 (in Debian Wheezy), I had problems remapping some keys on my eee pc 901's keyboard. In 4.6 (using Debian Squeeze), I had a script that ran as an xfce autostart that used xmodmap to remap the keys. Upon upgrading, when said remapping script was run as an xfce autostart, said script took about 5 minutes to run, with the attendant high cpu usage.
I found this to be unacceptable.
So, I put a call to the remapping script in "/etc/X11/Xsession", near the beginning of said file.
End of problem!
Xfce 4.6.2; Debian Squeeze