This started happening to me the moment my wife got pregnant with our first kid. Before that, even tear-jerker news stories didn't affect me; now, I get choked up over anything (but especially over hopeful science news stories - the Philae lander, possible breakthroughs in solar power, that kind of thing).

My wife makes fun of me for it too, but then I make fun of her for lots of stuff, so that's fair.