Honestly, I'm now almost at the end of S6, and I have to say the last two seasons have been a bit more hit-and-miss. The humor has changed a bit, which I don't mind, bu the way the moral is explained and hammered home is a bit much. B99 has always had the same sort of message, and I approve and all, but the earlier seasons don't end their episodes with 2-minute Serious Conversations About What We've Learned Today quite as much.
Will definitely watch S7 whenit's available, but...Maybe 7-8 seasons is enough? I feel like most comedy shows going over that lose quality - Scrubs, Friends, HIMYM, T70S, TBBT, almost all of them started losing steam around 7-8 and should've ended before 10.