I definitely fall under the Jack of all trades category. Being into so many different periods, with interest changing depending upon what time of day it is, it feels like. Unfortunately I'm also a bit of a completionist which makes things interesting (and expensive).
The result is that I've ended up with Napoleonics (a bit of 28mm but I'm finding I prefer 15/18mm so I've run off there and now have a bunch of lonely 28mm stuff that needs to be flogged off). World War II (Eastern Front, but inevitably have elements to do a half decent Normandy game as well), World War I (in 28mm, along with the complete Jutland in 1/6000 and a small set of aircraft to match), Cold War (3mm and 15mm, don't ask why) and finally, to let my hair down, VSF/Steampunk adventures, because for the kind of skirmish game IHMN allows you to make, a whole new force is frighteningly cheap and fast to make...