I went through about 5 years of being able to play nothing but a D chord so I kinda know where you're coming from. I think what finally got me out of my slump was first of all getting a decent guitar instead of my K-Mart $20 special with the warped neck.
Next thing was leaving my new guitar out at all times so that any time I felt the urge, I didn't have to go through the bother of taking it out of a closet or whatever, taking it out of the case, cleaning it off etc etc... It was always sitting there so anytime I got bored or was watching TV, I'd pick it up and try picking out notes. When I was living at home, it was basically sit down with your parents and watch TV or go to your room and listen to one of your 5 albums you owned and try to learn them. The secret is sticking with it and realizing that learning guitar takes months and years. A lot of guys give up after a few weeks cause they feel they aren't getting anywhere, but that's just the way it is.
Next thing was getting into a band. Even when I only knew a few chords and basically was terrible on guitar, I was auditioning for bands. Once I got into one, it forced me to learn 40 songs almost immediately. Basically, if I wanted to be in a band, I had to know a ton of songs, so the incentive was there to learn them whether I liked them or not. Once you learn a bunch of songs you start to realize that a majority of popular tunes are very similar in the way they're put together. Ie, an intro, verse, chorus, verse, chorus, bridge, chorus and fade. Once you've learned the intro, verse and chorus, you pretty much know the whole song.
From there it just kinda progresses on it's own. The more you learn, the more you want to learn more and other things start interesting you like reading music, tab and learning theory etc...