I tried to enforce them once with a precommitment service (i.e. you set up a deadline and pay money if you slip). The first missed deadline stressed me, which made me miss more deadlines, which got me even more stressed, thus missing even more deadlines, up until the point my credit card started bouncing. And mind you, this was on trivial tasks - I just couldn't overcome the anxiety and make myself do them.

I ended up an order of magnitude more miserable and in a very bad financial position for half a year. I can see how it works for people with big tolerance for stress (apparently I'm not one of them), but it's a double-edged sword.