Linux Flash support under PowerPC isn't a major breakthrough in general. While Adobe has not provided any PPC support, the Gnash and Swfdec projects have previously worked to provide PowerPC support and their ports work to varying degrees, but now Lightspark joins the party for providing newer Flash capabilities.
Alessandro Pignotti, the lead developer of Lightspark, says though that the current Lightspark for PowerPC implementation has performance that's far from ideal when it comes to video playback. This is due to an inefficient code path being hit, but eventually that will be rewritten.
The Lightspark 0.4.5.1 release announcement can be read on Alessandro's blog. This release also restores YouTube support, yet again, but doesn't really bring any other changes. Alessandro does note though that a new AMF3 parser will be merged soon to provide Local Shared Object "Flash Cookies" support.