If you're still trying to figure out what the heck to get the writer in your life, then here are a few suggestions:
Writing resources. My roommate, who has excellent taste, just got me The Best American Magazine Writing, which I plan to enjoy on my six hour flight later this week. Another favorite of mine is The Writer's Block, although admittedly I get more amusement from its unique shape than the ideas inside (still, it makes a lovely desk accessory). And a copy of The Writer's Market, aka the writer's Bible, will be greatly appreciated by any serious writer.
A blank book with a fancy pen. For t he record, I probably have enough of these to last until at least 2010; however, I always appreciate a pretty journal. Personally, I've been eyeing this Vera Bradley notebook, but a smaller version like this travel journal is infinitely more portable (and practical) for writers on the go. Pair with a nice pen like this one, and you've a got yourself a great gift set.
Gift certificate for a writing class. Sure, its less personal than a book or journal, but chances are it will be well received. Media Bistro offers tons of classes across the country (many online), and in Boston check out Grub Street or one of the many adult and continuing education centers. If they don't offer their own gift certificates, then design your own offering to pay for a class once the recipient decides which one s/he wants to take.
Happy Holidays, and happy writing!