Personally I think they went south a lot earlier than that, m'dear. I can't really pinpoint the exact timeframe anymore because all the episodes are jumbled in my mind and I can't remember which ones came in which order, but there was definitely a transition where they went from 7 or 8 out of 10 episodes being amazing and funny and clever with random surreal awesome jokes and the other 2 or 3 just being really really good, to not even managing to have more than 1 or 2 decent episodes in a season. And I'm not talking about post season 10 material, either, I'm talking around season 4 or 5. It went downhill really fast for me (though as always there are still a few unexpectedly good episodes in the mix there, you never have the same level of "hits" as you used to get).