When I need to I've found that separating different activities helps me from getting "caught up" in the Internet. I use a HTPC to watch tv-series/web-tv and listen to music, an android phone for connecting with friends, e-reader to read books and documents. If I do need the computer I mainly use my laptop without wifi, and plug it in when I need to access the Internet briefly.

I do use my desktop computer for gaming, surfing the web and other purely recreational activities, but at least I'm not kidding myself when I do. Before I would tell myself that I was doing something useful, while I would get into the "loop" you're talking about. Now I read and watch video less, but I read and watch things I actually like.