Have some dual-screen-setup containing of some ultra-fast AGP-card, being more
than sufficient for using composition and some old ultra-slow PCI-card, being
much too slow for using composition. 

When running this server-layout without Xinerama, I can say xcompmgr to manage
only the fast screen, and as a result half of my display looks incredibly great,
whilest remaining fast. 

When activating Xinerama, I cannot activate composition, because the the slow
card dictates the pace then. Well, and my slow card is that slow, that I can
watch the rendering line-by-line then. On both screens.

So me dream would be being able, to tell xcompmgr which Xinerama-monitors to
handle. So I could get eye-candy on the fast card, good performance on both
cards, and I could drag windows between both monitors again. Don't know, if such
a feature is possible, but if it is possible, it would increase adoption of
xcompmgr alot (especially, if it would launch into some smart-mode by default
and loudly refuse to manage slow monitors).

Thanks for listening,
Mathias