Having played mostly one shot adventures over the last month+ at Games That Can Not Be Named, I have a few thoughts on the matter.
One Shots are an excellent way to highlight a new system or a new adventure. It's also a great way to play test material that is not yet released and possibly work out the kinks.
They work great at Cons, as no one really expects to be playing in a campaign at a Con.
Most one shots work better with pre-gen characters in my opinion, which was not the case at most GTCNBN sessions. When you have a 4 hour block of playing time, getting a table worth of characters generated and answering a table worth of player questions can easily eat up that first hour.
Constantly playing one shots can lead to player attrition. Campaigns lead to a bonding: between characters, between players and between a player and their character. That bond assists in bringing the players back.
Of course, the whole purpose of GTCNBN was to play test new games, so the weekly one shots are understandable. I just think they lack long term sustainability.
Like I said, just a bunch of thoughts on one shots ;)