Plus it totally broke both the "YousableTubeFix" /and/ "Loopy for Youtube" scripts!
Turns out to fix it back to the regular layout you need to go to a specially designed video url, then kill your YouTube cookies, and even then I'm not sure how long that fix will last for...
What the heck is wrong with these idiots?? Hopefully someone will make a script to revert it if they're ever dumb enough to do a full forced switchover...