So I mark the subject as [closed] (but not resolved, since it has nothing to do with the initial suspicion)

have you tried to run fsck?

Thanks for your suggestion (I still dont have the right reflexes with linux) but fsck tells me it's clean (at least the partition where my /home is mounted). By the way, it's a reiserfs : could it be a problem from reseirfs and have nothing to do with xfce?

I have some difficulty to figure out where does my problem comes from, so please ask me some precision if necessary.

My system : standard xubuntu 6.06 LTS (so with xfce 4.4 beta1)

It seems to deal with the default app/widget/service used by graphical applications (openoffice, thunar, firefox...) to access the home directory (any file dialog typically) AND only when this app or dialog looks inside my home directory. First time I had this problem was with evince (see below)
Symptoms :
- I can hear my disk makes a few scratch a few times (in a "periodic" fashion) during 1 or 2 seconds, the system hangs during this time
- I can no longer use evince, it totally hangs the system when launched, "scratching" the disk indefinitely, in such a manner that the system becomes unusable (that is I cant even make a "ps" or log into a basic tty session to kill evince)
- no problem with access by terminal
- no problem (for the time being) with a new user I create (but I dont want to loose my config files so...)

This is really annoying as evince is the default viewer for many files. And the fact that it hangs the system lets me think it could be a serious bug. I have tried to look for a lock file not deleted, erased the ~/.cache but without success. Any idea what could it be or what's the next step?