I heard of this concept about a year ago when I went to visit Best Buy at their headquarters in Minneapolis. Basically, employees can make up their own hours. If you're a dad who wants to pick up your kids from school at 3:00 everyday - you can do it. If you prefer to work from home - you can do it. If you prefer to work at night - and sleep in the day - you can do that too.
At Best Buy - they have true "flexible hours" As long as managers and employees have realistic conversations about what's needed in terms of productivity - hours or place of actually working don't matter. Check out the CNN article about it.
Workers at the company had mixed feelings about it when I chatted with them a while back. In essence, it makes it very difficult to manage people. Managers actually get in trouble for making employees feel like they should be in the office - so it puts a lot of pressure on a manager to set very straight-forward expectations and goals of actual tasks. It also makes it near impossible to have "team conference calls" or mandatory meetings. (not to mention if you're a sales person calling into a marketing department. Having a large meeting is unrealistic)
On the employee side - I think it's great in theory - but only good in practice. Sure, making up my own hours is ideal -- but I think there is long-term value from going into the office and learning from others. I think over time it would feel a lot like school where you have an assignment and you wait till the last minute to get it done. I hated that feeling (personally)....