Kris Rusch did a post on having a will and a literary executor, and Passive Guy (who is a lawyer) chimes in as well. (Note that any executor position is a job. People rarely want jobs for which they are not paid.)
My grandfather was also a lawyer and was the vice president in charge of estates and trusts for a bank, so I certainly had the need for things like wills drummed into my head at an early age. (In fact, I first got a will when I was in my early 20s and had no dependents, which amused the hell out of some people.)
But I'm going to point out something that may seem a little contradictory: You can't predict the future.
My grandfather thought he could. He knew all the ins and outs of estate law, and he drew up a monster of a trust designed to virtually eliminate taxes and to ensure that no one in the family would ever be poor again!!!
The problem is, he drew it up in the 1970s. Tax law has changed considerably since then, so strategies that were supposed to save us money no longer do. Instead, they greatly complicate record-keeping and greatly increase the fees we have to pay lawyers and accountants. The institutions that were supposed to look after us no longer exist. Coping with all this crap is extremely time-consuming, and we are planning to petition the court to dissolve this trust as soon as it is practical because we don't want the next generation to have to deal with it.
So, while I do think you should certainly have a will, don't be a control freak about it. If, a century from now, your great-grandkid blows all your hard-earned money on drugs and winds up in the poorhouse, that's on him. There's only so much you can do.