My answer for "what do you want for Christmas" was flannel sheets, as these are reasonably inexpensive ($50 or so ) for an Xmas gift. It was a practical choice: I only had one set, they could be easily shipped via a catalog vendor (Land's End, as it turned out) and that they would fit even if I gained holiday pounds (unlike, say, a lycra cocktail dress). This was a wonderful gift, one that I enjoy every other week (when the other set is in the wash). But I probably can't ask for that again only 3 months later, plus, it will eventually get warm again.
I have all the books I require (remember where I work) and can't imagine asking mom for the new Momus or Magnetic Fields CD. Other than nebulous things that can't be shipped via UPS (central heat for my house, some flowering bushes to plant along the fence, various intoxicants, a sushi feast, a tattoo, a haircut that I'm happy with, a week's worth of Mom's etoufee), there's nothing I covet (other than Jon Stewart, but again, he cannot be purchased and/or shipped).
Materially, I'm pretty happy. I don't need Tivo, an iPod, any more DVDs, or gift cards (I still have one from 2 Xmases ago I haven't managed to spend yet). Lately I'm more interested in divesting myself of extraneous clutter than getting more/new stuff. But I don't want to seem ungracious. Mom surprised me many years ago with a lava lamp (she said "You don't know that you want this, but you want this"), but other than that, I seem to be difficult to buy gifts for if you aren't either in my immediate peer group, or a boyfriend (past or present).
I have the same problem with buying gifts for her. Many years, I don't send her a birthday gift, I just phone and wish her a happy birthday. But since I'm not married and have moved cross-country every 5-6 years, I think mom still thinks I'm itenerant and broke and that's the reason I don't send a gift, rather than the real reason that I hate to shop on deadline and am out of ideas. Plus, since she's twice my age and has the same antiquing/thrifting/estate sale-ing gene, she already has a house full of fabulous knick knacks and there's no way I could add anything to the eclectic decor of her house.
Now I think I understand birthday angst (especially at milestone middle ages like 35, 40, 50, etc)-- when you're young and it's your birthday, you desire a pony, or an Atari/Nintendo/xbox (choose based on your generational cohort). When you're college-age, you want money to splurge on an outfit/concert tickets/rent. The older you get, you can afford your own "toys" and neccessities, and the things you REALLY desire (the body you had five years ago, better health, more leisure time, a partner that loves you, a life of fewer regrets) are intangible, and not for sale at any price.
I guess I could use some new slippers, though.