ANYONE???
FWIW, I seem to be having similar issues. Used 10.0.3 for the first time earlier today (under Snow Leopard, on an 8-core Mac Pro now with 24GB of RAM). Constantly losing video -- audio plays fine. Never seemed to have this problem in 10.0.2. (Lots of other problems, mind you -- just not this one.)
Found I can usually get video back by opening Playback Prefs and making a change (like switching between "use proxy media" and "use original/optimized"), then waiting 2-3 minutes while the orange bar which has now appeared over the ENTIRE timeline -- even though NO changes have been made to the timeline whatsoever -- slowly goes away.
One of the triggers for losing the video in my case seems to be letting the Timeline play through till past the end. And I say "past" the end, because there's now suddenly a weird 2-3 minute void after the final clip of video. No audio, no "gap clips", just a big stretch of nothing. I can't figure out how to get rid of it, and the fade out I'd applied long ago to the last video clip no longer works. When the playhead reaches that transition (or nears the end of the last video clip, even with the transition removed) the video just cuts to black. The audio then ends normally while the playhead just keeps going into this mysterious blank emptiness for almost 3 minutes -- at least that's how much extra black I get when I do an Export of the Project.
Naturally I've tried re-doing the end transition; and have of course made sure there is no media of any kind down at the end of timeline which might be causing this strange empty section. Even tried carefully selecting all the real clips on the Timeline and Copy/Pasting them into a whole new project. No difference. The gap at the end just reappears.
(Meantime, as others have reported, I also experienced loss of parameters on several simple titles in Projects created in 10.0.2 and updated/imported into 10.0.3. Likewise for the irrational re-re-re-re-re-re-re-re-re-re-re-re-rendering. Have not yet had time to test any of this on a newly-created 10.0.3 project, but I really do look forward to the day when the bulk of my work in FCP-X might actually involve editing, with the time spent in trouble-shooting and unpaid beta-testing perhaps reduced to just a few hours a week. A crazy idea, I know -- but I can still dream.)
John B
Toronto