How Long is too Long For a Family Vacation? [POLL]

Some friends of our just got back from an amazing vacation. They had a great time but they both admitted that they were gone way to long to the point were everyone wanted to kill each other the last few days. This was not a good way to wrap up their vacation.

Vacations can be tricky, you don't want to be gone to long and you defiantly don't want to make your vacation to short. So what is the magic number of days and does it make a difference if your kids are with you or not.