My wife and I usually plan big vacations about a year in advance so that we can follow flight prices and whatnot to get a good deal. We also book a few days at a cabin for our anniversary every year, so we just book the next year's reservation while we're there, since reservations can fill up even several months in advance.
Only planning a week in advance seems stressful to me - we planned a last-minute (for us) road trip vacation earlier this month for the long 4th of July weekend, and it was tough to find cheap places to stay that weren't super grungy.