Now, atheists will tell you that atheism is not a religion. Technically it’s not, but many of them sure act like it is. All you have to do is jog on over to richarddawkins.net and you’ll find many individuals, who with a slight change in beliefs, would fit in very well at a camp revivalist meeting.
As an atheist myself, I have to agree. Around this time I'm always ready to say "not this crap again." I think, honestly, who do these billboards help? All this does is needlessly attack a religion, piss people off, and make the authors look petty.
And they even got it wrong! Christmas isn't a myth, it's a real holiday celebrated every year. Now the origins of it, that's a different matter.