Just off the top of my head a small list of things
@Lowtax had the chance to get on the ground floor of but never did because of reasons. I'm certain other can add to this.
Mega64
Zero Punctuation
4chan
Let's Plays
Reddit/Reddit Style AMAs
Podcasting
He's had a number of things fall into his lap but is just too lazy to capitolize on it.
I've no idea about Mega64, but none of those other things come from SA directly.
Yahtzee put a couple of videos up on Youtube and was offered a job at the Escapist based on them. Plus he had his own website full of comics and games that he'd made years before posting on SA.
He had his Chzo Mythos game series (that started on the Adventure Game Studio forums, not SA).
4chan was modeled after Japanese imageboards and would have festered and died if it were behind a subscription wall (plus, there's no way Lowtax would have put the effort in to implement an imageboard like 4chan within SA, he's such a lazy retard that he likely wouldn't even bother reading a description of what an imageboard is).
Leaving SA to create 4chan was the best decision moot ever made.
Despite what retards on SA say, "let's plays" were inevitable even without goons making them. Playing videogames is one of the most popular hobbies on the planet, and people have enjoyed watching people play them for as long as they've existed. With the advent of free video sharing services like Google Video and Youtube it was inevitable that people would start uploading let's plays to the internet.
None of the popular SA let's players are really that well known outside of SA and related communities, either (Chip and Ironicus, one of the most popular SA let's play channels, only gets 15k-25k views per video within the first couple of weeks - this is despite putting out content of a decent quality consistently for years).
Retsupurae is probably the most popular SA LP thing, and they're only big because of their Youtube audience.
AMAs aren't a unique thing to SA, it's just people talking to each other over the internet.
Podcasts became popular with the fist gen iPod, that's where the name comes from. Are there even any mainstream podcasts that have goons on?
If anything, I'd say that the key to success for goons is
not using SA and moving to outside platforms.