Even if you don't want or don't need any achievements this year, Winter Veil will also give you the opportunity to turn your mount into a reindeer, become a snowman with a unique dance animation, and get noncombat pets and unique holiday items. Interestingly, it looks like the Winter Veil pets no longer require snowballs to summon, which is cool, although they're not going to stick around if the holiday's not on. Seriously, go try pulling out your Father Winter's Helper and see what it does. I'll wait.
There's also a new pet as of 2011 and a sorta-new (well, not really) holiday boss. As always, I'll be up as the holiday goes live to make necessary additions or corrections to the guide.