I hate them, they can create snow in protected areas, they're annoying to deal with and easy to grief with. It would be nice to have a light weight plugin that just simply blocks their creation, that's it.
I think that's possible via Multiverse. It has per-world setting of mobs you wish to disable. If you add snowgolem they won't be spawn-able, not by eggs/commands/building.
essentials, multiverse, worldguard plus many more do this http://forums.bukkit.org/threads/req-snow-golem-fix.47090/ EDIT by Moderator: merged posts, please use the edit button instead of double posting.
World Guard and Essentials both do not do this, as far as I know, I think the plugin listed there is not supported in later bukkit versions, I'll test it later.