I've gotten rid of a lot of the time-wasting sites that I used to spend so much time on, but I'm still a little in awe of how much time it's freed up. I deleted Tumblr a couple of months ago but I still find myself casting about for things to aimlessly scroll through on the internet. I barely use Livejournal at all any more, and my Facebook is just a way to keep up with a small handful of people, literally about three or four, that I don't have any other way to talk to. They only update with about 8-10 new posts every day so at worst, I'm just wasting ten minutes.
The funny thing about it is that after I've exhausted every other site, I usually just come here to doodle around and write something, and then I end up being productive because I'm updating my blog. I don't consider this cheating - running a blog properly is something I've been wanting to do for years, and I typically end up dropping (too busy refreshing Tumblr), so every post is a victory as far as I'm concerned. If I'm not writing here, maybe I'll play a bit of a video game that I've been working on, which again is productive for me since I have wanted to get better at video games for years.
What I'm seeing from this is that it is worth putting thought into picking the things you do. Going to Tumblr or Livejournal becomes a habit, but really, just about anything can become habitual. If you want to be productive, pick sites and activities that are purposeful and valuable to you and relate to a goal that you have. At the end of the day you aren't going to just sit and blankly do nothing - you're going to find something to occupy your time with, and it's going to be the things that are most immediately accessible. If you make sure that those things are valuable, and put purpose and thought into choosing them, you're going to end up doing those things as regularly as you did Plurk and Pinterest. Except that you're also going to progress, instead of spending all afternoon scrolling through image posts and other people's personal updates, and realizing that you're in the exact same place and you're the exact same person that you were three hours ago.
Think about it: in three hours you can work out, write a blog post, drink a cup of tea, make pretzels, and defeat a level of a video game. You can get hooked on a new novel. You can clean your entire apartment; watch three documentaries; complete a chapter of a Teach Yourself language course. If you keep these kinds of things beside you on the table or the nightstand or your purse while deleting Tumblr and Facebook from your favorites bar or your app list, you'll turn to the things that are valuable to you in order to occupy your time just as easily.
Now I've written a blog post, and I'm going to go and make pretzels.