I dunno about you guys, but whenever it gets cold, like it is right now in much of the USA and North America in general, my choice in books changes dramatically. I tend to read longer books, and I tend to read more genre stuff, particularly long SF and fantasy novels with big secondary world settings. In the summer I tend to read shorter, more fast-paced stuff, thrillers and shorter literary works plus the odd nonfiction book, but if the temperature drops below 50º F, I'll read bigger, slower, more elaborate novels set on other planets, or the past, or some fantastical setting.

Of course, those books are sometimes a lot more fun to read if you're lying under three layers of comforters because it's just damn cold outside and there's no point in going anywhere.