I've heard that the average traveler gets the most joy out of any vacation about 6 weeks prior to the trip. Yes, that's right. A vacation is the most enjoyable 1.5 months before you take it.
At that point, I guess you're still working with expectations. You're able to be really happy and excited about it, without the whole issue of reality setting in.
As you get closer to the departure date, you start thinking about the little things. The "what do I pack?" stuff and the "will I look okay in my swimsuit?" freakouts. But not when it's still weeks away.
When the trip is weeks away, you get to plan, and consider the possibilities, and build up the expectations - which, according to that same study, most vacations never quite live up to. And that's why the during AND after times aren't as highly regarded as the 6 weeks before.
So... As we start planning, I think I will also plan to bliss out a little over the fact that summer is almost here - and so is vacation.