This actually works very well. I don't have an ipad yet, but I do the same thing with my iPhone. In addition to that I also have leechblock(found it in lifehacker) that blocks 3hrs block of time with breaks in between. 8-11, 1-4, 6:30-10:30 and midnight-4am. This way I can't "accidentally" browse HN or other news site during my supposedly productive hours. If I really need a fix, I just browse in my iPhone and away from my computer. It's easier to stop browsing on my iPhone than on my computer.