I'm never more than 5 seconds away from a Google search interface. This is incredibly valuable about half of the time. The other half of the time it drops a giant anvil on my productivity.
Many times per day, interesting items from Twitter, RSS feeds, and, occasionally, an actual human conversation send me racing to the search bar. Often, that search leads to something else, which leads to something else, and so on. I'm sure you've all been there.
There are worse forms of entertainment than semi-aimlessly wandering the Internet. The problem is timing. Interrupt-driven wandering breaks my focus away from things that are more important to me.
Whenever I start a new pocket notebook, one of the first things I do is create a two-page spread titled "Check Out." It started as a place to park interesting things I see on the go, because my kids JUST. WON'T. WAIT A MINUTE. (Sorry, I've regained my composure.)
Over the last month or two, I've started using my "Check Out" list a bit differently. In addition to jotting down interesting things I see in the wild, I now use it at my desk as well.
I still do plenty of spontaneous web browsing, but I try to be more mindful about it. If I feel like I'm about to step into a time sink hole, I pull out my notebook, add an entry to the "Check Out" list, and get back to what I'm doing.
I revisit my list every couple of days, generally in the evenings. I'd probably be browsing the web at night anyways. The "Check Out" list gives it some direction.
Another thing that I've discovered is that I lose interest in about a third of the items on the list by the time I get around to researching them further. So, this is effectively time that I would have wasted in the moment that I've now gained back.