Sure, I suppose it couldn't replace every payment like this from needing to go through a lawyer. I suppose if you wanted to send 10 billion over seas to someone in 20 years, you might want to seek some legal input. But say for the simplest case I just wanna set something up that sends some money to my child on his 18th birthday I could use a smart contract like: https://www.reddit.com/r/ethereum/comments/4ww0sr/need_a_con....
You're placing a heck of a lot of trust in a digital system if you're putting a significant (as in "I would hate to lose this") sum of money into it in the expectation it'll still be there in the future.
Even if we put aside the problem of unstable valuation, forks, and potential total collapse of cryptocurrencies, you're going to face the challenge of keeping a private key secure for however many years you plan to escrow the money.
Compared to creating a trust account, this is insanely risky - you'd have to be convinced that the legal and banking systems were facing imminent catastrophic collapse to think that's better than what we've got.
Again, where is the problem? If you want to send money to your child on their birthday, just send it. Why do you need a contract, 'smart' or otherwise, for that?
Edit: What's funny about that thread is that it's someone asking for help to get a contract written (...like you do when you see a lawyer), and there's supposedly (or not, unsure about the sarcasm) a venerability in the contract itself.