My latest big obsession, one of the biggest obsessions was Google SketchUp. I took 2 years with 80% of the time I used the computer just playing with it, creating models. I even got some buildings to show up on Google Earth's cities... Nowadays I rarely run the program.
The latest little obsession I had was about beer. I suddenly started buying all types of beer just to compare the tastes and origins! Now it is gone, but I still like to drink a good German beer.
The obsession I am currently in is about IT, but I was once obsessed with computers before and it was big, but now I'm re-living it and much more intense, it's probably going to become the widest of all obsessions I had.
Another obsession I am currently involved is about Aspergers, probably because I recently discovered what it is and that I have it...