Well last year we went for about 2 weeks, we also did Universal for 3 days. This was only the 3rd time with my kids, 1997, 2000 and then 2005. My kids were 14 & 17 on this last trip and I have to say that they were ready to leave when we did, probably before.
I think they were anxious to get home to their friends. Also, even though they enjoy it there, there was a "been there done that" kind of feeling for them. I'm almost afraid to admit that I sort of felt that way too.
I think the next time we go it will be just my DH and myself and we will "do" WDW much differently. Much more slowly, enjoy the resort more, etc. I may get my youngest to go back again, but I doubt that my older son will want to go back. I'm hoping that when he has kids, he will want to take them there and maybe grandmom can tag along !!