same issue - mostly happens when copy/pasting objects. screen flickers black and system becomes unresponsive with nothing to do. depending on the number of objects it sometimes recovers (one box for example) after waiting long enough, with more objects, no way.

edit: macbook pro 15", 2.53 GHz, 4GB, 10.5.8, OG 5.2 (v138.9.0.117994)