I've always gone for two weeks. After the first week I just start to feel like I've really hit my stride, but I have to admit by the end of the second week my body does let me know that this may have been a little bit too much. Ten days looks like it should be the sweet spot.
May be my issue as well,it takes me a few days to forget about work, and my brain always starts to think about it again as the vacation in running down.
We have done 11,10,9, then 8... we are going back to 11. 10 was probably the best amount.. still hated to leave, but we were thoroughly worn out. The hardest part for us was when our friends leave after a week you have a new fresh crew coming and you are wearing down... you have to stay in the right frame of mind and make sure to make friends that will be there as you or after you so that you aren't all depressed on the last day.
Groups changing over is hard when you do 14 days. First trip we lost a great bunch of people after about 5 days, and then met another great couple we really bonded with on our last day! There was a definite divide in our trip in November: from those already there and left in our first week, and those who turned up after us and we left before them. It's good to try and match your dates with those you party hardest with!
