The Mac Pro/ATI Radeon X1900GT video bug after overnight system sleep discussed in the March 1 entry occurred two nights in a row with two monitors attached. Leaving only a single monitor attached (Apple 30" Cinema Display), the problem did not occur this morning. (So far I have only three nights testing, and overnight sleep is needed to induce the problem).
Of course, those are small sample sizes, and it’s hard to be sure that’s the key factor. Next I’ll try using two Apple-brand displays, instead of the 30" Apple Cinema Display and the 24" Sun Microsystems display.