There doesn't seem to be any snow in my current minecraft worlds, although I haven't explored huge parts of them yet, so I guess it might still show up. Are snowy biomes just really rare, or is there a bug causing them to not be generated at all?
The terrain generation code was completely rewritten for 1.8. Whether it's a bug or intentional, you're right — there are no snow biomes in Minecraft 1.8, at all.
Minecraft 1.9, which will be released in the near future, re-introduces them, though. The pre-releases of 1.9 already generate snow biomes, so it's a pretty safe bet.