How do you get out of a boat in Minecraft?

What I normally do is the same as I do for minecart stations: put a minecart on a rail on the shore, then surround that with half blocks. You can then right click on it from the boat, magic-ing you into it and not disturbing the boat. It might not be what you are looking for, but it is simple and works well.

I've found that boats are less likely to go shooting off into the distance if you get out of them where water is only one square deep. It's not always perfect, but that, combined with looking straight down when you exit, usually prevents a boat from flying away and crashing into the shore.

I have found just getting out of the boat while it still has some bare minimum momentum and letting it slide out from under me to have perfect results, in that I don't bump it and have to chase it across the ocean :)

Make a dock out of soul-sand and run your boat into it. It won't immediately break against the soul-sand, unlike other materials, and once it is stuck in the soul-sand it will stay put unless you shove it out.

You're not missing anything... happens to all of us.

Row to shore, so the front of the boat is touching land. Then look down at the boat and right-click, as Jasarien suggests, and back out of the boat, so it is "pushed" towards shore. It should barely move, if at all.

Make sure you enter straight, or else you'll spin around unpredictably. If the boat is completely still, you don't need to do the space+arrow manuever. Just don't move, click on the boat to get off, and jump. The currents keep the boat stable and in the spot you leave it for future trips.

It isn't quite as elaborate as docks with doors, but it does involve some tricky currents so your mileage may vary.

Source: Boat Science on MC Forums

Make a channel one block wide with dirt blocks and drive into it. Not too easy, but effective.

I use the Soul Sand technique described by Zoredache, but you might want to carry food with you on your boating trips, because the Soul Sand dock sometimes glitches up and deals massive damage to your health, sometimes killing you in one hit (although food is pretty much worthless if that happens). It seems like damage that would apply to a boat when crashing into other things, applies to you when crashing into Soul Sand.