My friend K. is obsessed with Finland. She is Japanese and lives in London but flies Finnish air everywhere--even if it means the most roundabout flights--has memorized some handy Finnish phrases, and at any point in the year can tell you the price of a round-trip ticket to Helsinki.
Now I have plenty of friends with obsessions: C3 hates cilantro, D. can't get enough of political speeches, and L. for a long time was obsessed with bringing down dvdandmedia.com.
But I listened to them go on about these things with only half an ear open, as none of these things benefit me.
Except for K. Her obsession has yielded this: the Karl Frazer chocolate bar (the disco showroom lights are my extra special touch). In my choco-meter this ranks well above Cadbury's and just a wee notch below Lindtt. (Oh, and 50x better than gravilax and cabbage rolls.)