Really hard. I should also clarify: with 2 kids 3 years and under. I think (hope?) it gets easier once they are school age.
First. There is The Issue of All of the Stuff. Seriously...kids need so much stuff when you go on vacation. And it doesn't matter whether it is for one night or two weeks. Stroller, sling, diaper bag essentials, car seats, portable crib, toys, snacks, blankies.....all must come with.
Second. There is The Issue of Lack of Sleep. No matter how great your routine is at home, travelling shakes it up. Nap times are interrupted, sleeping arrangements are different. For the trip we just got back from, sleep was particularly hard for C-Man because he is still sleeping in a crib at home, but had to sleep on a makeshift futon thing-y in a loft above a bright, noisy living room.
Third. There is The Issue of Cranky Parents. This stems from two things: lack of sleep (see above) and the Memory of How It Used to Be. You know what I am talking about, parents. The neatly, expertly packed carry-on, arriving at the airport within an hour of take-off. Thumbing through a magazine on the plane, listening to music or better yet (gasp) snoozing on the plane. Drinking cocktails or delicious wine once arriving at destination, having lots or great conversation with friends you never get to see. Sleeping in. Restaurants. Art, movies, shopping. Remember those days? What? You say you don't have kids and still have those kinds of vacations? Go away. Just kidding. Come back. Just have pity on us parentals.
My attitude is already getting better about our trip (I know you can't tell from this post). It is still nice to get away and be together in a different environment. And we still had time and the energy for a little of this: