Well, for me, I am not worried with the spoilers ONLINE affecting the show's rating. Majority of TV watchers, they don't spend that much time online, or search on-line for spoilers. I think its really a small minority of us RABID fans that search the net for spoilers. Most of those numbers that view the online spoilers are from different countries, that's how popular New Girl is. I was one of them, the first season, I watched it only online, since it was not available to where I was last year. I have 4 friends here that is an avid fan of the show, but they are spoiler free, since they not as rabid as me, wanting to be spoiled and such, hehe!!
Plus, we are a great example of those dedicated fans that even if we have watched almost the entirety of the show through spoiler-y previews, we are still going to watch the actual airing, hehe!
