I'm good at getting things out of sight. I've been contributing to 401ks and IRAs from a really young age. And I never even think about that money. I literally forget about it. But I also (up until recently when my exit from the workforce put us in abject poverty) always set up direct deposits so a portion of my paycheck would route into a savings account and it just never seems to build beyond like $1000. We'll get it up there, and then some expense will pop up like we'll need to replace the tires on our car or we talk ourselves into buying, you know, a grill or something, or I'll study abroad for a month. We'll knock it down and it'll build back up and then we knock it down, etc. The important thing about the IRS savings account, though, isn't so much that it puts it out of mind, it's that it puts it out of reach (I never would have studied abroad without it).
I used to be pretty bad. I just kick myself for having any debt at all. For years my wife and I were both working, making decent wages, had no kids, incredibly low rent, and no car payment. And we just spent like morons. AND we still managed to use credit cards in spite of having so much disposable income. Just inexcusable. There was a point when I could have been putting $1500 a month directly into savings if I didn't have a bunch of credit cards that needed to be paid off. I was, in fact, paying $1400 a month toward credit cards (about $1000/mo above minimum payments). We've certainly got our spending in check these days. I just kick myself for not having more discipline in the past. Things would be so much easier now.
But yeah, self-discipline is unquestionably superior to IRS-based forced discipline. But the latter, I think, is superior to no discipline or poor discipline. If one of the latter two apply to you, don't let the principle of the IRS thing deter you. The most important consideration is the reality of your own deficiencies. The IRS isn't the most efficient use of your money, but at least it's not the least efficient use. And, to be honest, I think that my conscious decision to have smaller paychecks in order to make use of the IRS savings account was in many ways a turning point for me. I was making short term sacrifices for long-term benefits for just about the first time in my life. I really think that saving through tax withholdings actually made me start treating finances in other areas more responsibly.