It was one of the reasons and an inflection point. I remember the rush of activity with the release of the platform. People were poking each other and sending game requests. These were all FB apps. It was one in of a string of hits by FB, creating a lot of goodwill. They quickly released FB to many languages, often crowdsourcing them.
I'd argue it was the apps (and the publishers) that led to the decrease of organic posting in Facebook. Instead of seeing posts from your friends, now you see viral articles, and app-related statuses.