This is a long comment constructed entirely of disclosure and discussion of personal data. Read at your own risk.
In the fall of 2009, I started using the program hamster to track first all the time I spent wearing pants, and beginning in 2011, all my time, 24/7. I initially did this because I felt I spent too much time on Reddit, on my feed reader, and on email lists, and in general, wasting time. I thought that by tracking my time, I could quantify how much time I wasted, and reduce it over time. This didn't work out, but I still enjoy having the data and can occasionally do cool things with it.
Reddit dwarfed the other activities in my waste category, and even my time usage at large (the single-most activity in 2010 is reddit, at 281.5 hours -- spending time with my romantic partner was second at 273.4 hours). My reddit usage peaked in August of 2010, when I spent 39.75 hours on reddit.
At this point, I quick reddit cold-turkey (I spent five minutes on reddit in december of 2010). I assumed that since I now had the single-largest waste time activity eliminated, I would be hugely more productive. This didn't turn out to be the case. As I stopped using Reddit, I started playing video games with friends I lived with. I've spent much more time playing video games than I ever spent on Reddit -- from 2010 to now, I spent 287 hours on Reddit, and 724 hours playing video games. I rationalize this by saying that most of this (534.4 hours) is "social" -- that is, I'm playing video games sitting next to someone in meatspace. But ultimately, I'm still wasting time.
The lesson I've learned from this is that it's futile to try to optimize away all waste time. Humans are not resilient enough to be productive 16 hours a day with current productivity systems. If I could find a way to accomplish meaningful work while playing Halo: Reach or browsing Reddit, I possibly do lots of good things. But I still wouldn't move through my todo list any faster.
Together, video games and my main romantic partner account for 1,571 hours of my time from 2010 to now out of a total of 9,888 hours total (time spent sleeping is only tracked starting 01/01/2011 and accounts for 2,075 hours). While it's easy for me to think of these things as non-productive, they're probably essential to my life as it is now. My romantic partner is incredibly important to me, and video games are the primary way of bonding with the people I live with (especially since I don't drink). Without those things, I think my life would be worse off.
This data is probably incomplete -- a better metric would be the rate that I go through items on my todo list. Since I haven't found any task software that's as good at what it does as Hamster is (I use Getting Things GNOME! now, the daily builds are tolerable), I can't examine that data. But if you're actually concerned about misusing your scarce resources, track how you use them and decide based on actual data, not based on how high-status sex, drugs, and World of Warcraft are on websites.
I apologize for zeroing in on a triviality, but Is "wearing pants" a euphemism for something? Or do you normally sit at the computer without them?
I've avoided playing World of Warcraft because many people enjoy it so much that they neglect other things in their life.
Does that make sense?
How about cocaine?
How about sex? I hear that's pretty good too.
ADDED: Lots of interesting discussion, but no one is getting at some points of particular interest to me. Most answers assume that you have important stuff to do, and you need to decide whether WoW will prevent you from getting that important stuff done. They also assume that your brain usually errs on the side of telling you to do "non-important" stuff (WoW) at the expense of "important stuff".
One question is whether there is any evidence that your brain is biased in this way. I think your reflective self greatly overestimates the probability of success at the "important stuff". I have worked very hard, twelve hours a day, 7 days a week, on "important stuff" for most of the past 30 years. The important stuff never pans out. So it appears that when my brain told me to play Freecell rather than work on that important paper on artificial intelligence that got pulled from the book the day before publication due to petty office politics, or to watch Buffy rather than do another test run of the demo I spent three months preparing for DARPA that no one from DARPA ever watched because the program officer was too busy to supervise his program, or to go hiking instead of spending another weekend working on the project for NASA that was eventually so big and successful that my boss took it over and then tried to get me fired1, or to go dancing rather than work on the natural-language processing approach that got shelved because my boss felt it emphasized the skills of mathematicians more than his own, or to LARP rather than put in another weekend on my approach using principal component analysis for early cancer detection that it turned out some guy from the FDA had already published 6 months earlier, or the technique for choosing siRNA sequences that a professor from George Mason already had a paper in press on - all those times, my brain was using a better estimate of success than my reflective self was.
Another question is why the "important stuff" is important. Fun is fun. On the surface, we are saying something like, "I have a part of my utility function that values contributions to the world, because I evolved to be altruistic." If we really believe that, then for any contribution to the world, there exists some quantity of fun that would outweigh it. And people use language like, "WoW may be fun, but it has little lasting effect." But when you contribute something to the world, if the relevant motivating factor to us is how our utility function evaluates that contribution, then that also has little lasting effect. If you do something great for the world, it may have a lasting effect on the world; but the time you spend feeling good about it is not as great - probably less time, and a less intense emotion, than if you had spent all the time accomplishing it playing WoW instead. So this question is about whether we really believe the stories we tell ourselves about our utility functions.
1. He got to award himself all of the department's yearly bonus money that wasn't awarded to his subordinates, so any obvious success by his subordinates was money out of his pocket.