There's some replays at the end of the post.
Watching the stream of the FFA has immediately taught me one thing: most people don't know how ridiculously awesome scout/arbiter is when you have infinite money and attacking early means you die.
There is no counter to scout/arbiter. Air units? Yeah, right.... The only one that could work (unless you snipe all the observers and use cloaked wraiths AND your opponent doesn't just recall away from your wraiths) is valkyries but they don't shoot on BGH 90% of the time because of the sprite limit. Even if you have a far superior force half of it ends up frozen in blue crystals while the other half gets raped by missiles of doom for more than 30 explosive damage per attack. It turns out this even wins vs muta/devourer, even when outnumbered.
Ground units? No, they don't work either. In big numbers scouts have the advantage of being an air unit so they always get all their attacks off. Even goliaths end up losing since you stasis half the goliaths (and you can't EMP arbiters when scouts vaporize any science vessels with the same area code) and then you have four times as many scouts attacking as goliaths attacking because you have half of the un-stasis'd ones too far away to attack. Don't even think about trying hydras or dragoons.
Even if goliaths do win vs scout/arbiter, they're never going to break your cannons, so you can just ignore the goliaths. The cannons you'll have because it's BGH and you can build a million cannons with your billion extra minerals because you're going scout/arbiter off three gas.
Storm doesn't work because scouts move too fast and they have tons of HP. The only thing that beats scout/arbiter is ... scout/arbiter!
(Post inspired by me holding off a 180 food Z army and a 190 food battlecruiser army simultaneously, then another 180 food zerg army right afterward, then losing because carriers suck (I should have just stuck with scouts)).
Also, going scout/arbiter means you can do this:
Replays:
http://repdepot.net/replay.php?id=34546 (this is the one that shows real scout/arbiter play and me switching to carriers then instantly losing because I lose my carriers because they suck. I'm yellow.)
http://repdepot.net/replay.php?id=34547 (this is just generally entertaining; I noticed my scouts were better than my carriers. Also features nukes. And turrets.)
I should start using recall more, it means your already-mobile army is never caught out of position.