Well, so far it looks like it is working quite well. The half dome cables permit request period is 15 days in, and so far it seems like it is working as planned. As you may remember, in the past half dome was getting severely overcrowded on the cables and it was creating many safety issues. Last year, the Park attempted to implement a permit system that would limit the number of visitors to the cables to 400 total per day. The problem was that scalpers were able to purchase large quanitites of the permits then sell them off at a premium. The park service wanted to fix this problem, so in 2012 they have implemented a permit system much like Mt. Whitney's. There is a 30 day period to request permits, then the permits are allotted and applicants are notified of the results. So far it seems like both problems of the past are being solved; they will be able to limit the number of users of the cables to 400 per day, and the permits seem to be readily available and easy to acquire for those who have planned ahead. Nine days into the permit system, no single day has sold out yet. It seems like barring something unusual happening, the majority of people will get their first or second choice of dates.
Here are some charts showing the requests per day of the week, plus the number of permits requested for everyday of the permit season.
http://www.nps.gov/yose/planyourvisit/hdpermitsapps.htm
My wife and I requested July 6th or July 5th, and were very worried about being able to land a permit for the week of July 4th, however, this chart shows that the results look favorable.