Hmm... I decided to give it a try, based on what I read so far in this thread.
Currently, I am running total 26 Gnome-Terminalx in my desktop. 14 of them echoing "fortune -s" string, in every 1 seconds. 2 of them running 'top' command. So far, I have been running them about 18 hours. No slowness of any kind is noticeable. Neither does any of my applications (like firefox or OpenOffice Writer) has any problem.
Before I start doing the experiment, the system has been running for > 4 days (this desktop PC is also a tor router, so most of time, I let it run continuously, even when i am not using). My desktop is Dropline GNOME, but using Compiz-Fusion instead of Metacity. So far, no system freeze of any kind.
However, IIRC, it did freeze when GL's base screensaver was enabled (that happened a few weeks ago). But, is not something that I would concern much, since I am not that fancy of screensaver. I have not enabled screensaver since then.
$> uname -simpro
Linux 188.8.131.52 i686 Intel(R) Pentium(R) D CPU 2.66GHz GenuineIntel GNU/Linux
$> glxinfo | grep renderer
OpenGL renderer string: GeForce 8500 GT/PCI/SSE2
$> head /var/log/Xorg.0.log
X Window System Version 1.3.0
Release Date: 19 April 2007
X Protocol Version 11, Revision 0, Release 1.3
Build Operating System: Slackware 12.0 Slackware Linux Project
Current Operating System: Linux orion 184.108.40.206 #1 SMP Sat Jul 5 23:36:01 SGT 2008 i686
Build Date: 09 May 2007
Anyway, will let it run for a few more days...