With task-oriented work, you're either done or you're not. This is great when the task is small and you can be done by lunch and then do whatever the hell you want. O hai, I have finished reading these proofs, you wanna go to the Purple Onion? When the project takes weeks or months... you're kind of screwed. I mean, yes, you can set yourself a very disciplined schedule of 8 to 5 (or whenever) so that it's like you have a time-oriented job. But you'll be sitting there on Friday night or Saturday afternoon (cough) thinking, I really need the money. I'd really like this to be over with. What am I really doing here? Watching random true crime crap on the Investigation Discovery Channel? It's either this or go scrub the bathroom, really. And the other thing about task-oriented work is that you're not pulling in a regular salary; you don't work, you don't earn (ask my bank account). You feel guilty, like you don't have a real grown-up job like other people, unless you're visibly beavering away at something, unless you actually have a check in hand to show for it. So... work on the weekend it is.
The one good thing about this is that when you really have finished a huge project--say, a book--you are perfectly within your rights to take off--take off as much time as you want, or at least as much as you can afford. When I finished writing the Fifteen Minutes book--which took nearly a year and ran over at least three deadlines--I sat there for the month of June determined not to do A GODDAMN THING. Which is a great feeling, let me tell you. It's just... really not the feeling I get to have right now.