We are just in the middle of a 2.5 week road trip to California (including 6 nights at DLR), followed by a 2 week Caribbean beach holiday.
This is our only holiday this year, and the costs were paid over an extended period of time (multiple flights - BA miles and cash, numerous hotels, car rentals etc), but I think the total cost must come to over 30% of our net annual income. I certainly don't think we'll be doing anything similar again.
California isn't cheap, and we probably spent less than half as much for 21 days at OKW last summer. But it has been a great trip so far, and you can't take it with you