How do you get out of a boat in Minecraft?

The easiest way I find is to look directly downwards, right click to exit, and then carefully hop from the boat. It still moves, but not so much.

Perhaps Mojang may address this in a future update? It might be worth going to the Get Satisfaction page for Mojang and seeing if it's been raised as an issue already. If not, raise it.

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.

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.