I'm told in comments there is a crisis of epic proportions on Facebook that has naturally spawned a new Facebook page! Okay, putting aside Facebook users' tendency to match the outrage of the day with a corresponding Facebook page, it seems this time there is justification for PPC users as Facebook will no longer play flash videos unless you have the current Flash 11.1 installed (and Adobe's PPC support ended with 10.1). There's an ingenious fix detailed in this Youtube video, however, where the creator has made a modified Flash plugin to report itself as 11.1 even though it's still 10.1. Lo and behold, Facebook videos now work.
The direct download link is here (with a ReadMe included): http://www.steelbin.com/FPforFBPPC.zip
I've read several reports in forums saying it works, though I can't verify it myself since I don't do Facebook. Also this probably has security holes you can drive a tank through, but luckily there don't appear to be enough PPC Mac users to attract the hackers of the world.
That Facebook page for PPC Macs above might be worth keeping an eye on, too, as there may be more issues popping up in the future.