Oh man, how I love to collect used Christmas cards from coworkers, family, and friends. I have made so many beautiful things over the years.
How I reuse the card depends on the design. Some cards can be cut up to make gift tags for next year. I have used some to make bookmarks. To make the tassels, I found a craft book that teaches you to make it from ribbon but an easier way would be to use tassels from curtains or pillows you aren't using anymore. Then make a hole in the top of the bookmark and attach with embroidery floss or thin ribbon. If you have someone in your life who loves to read, what a nice compliment to a gift of books or even a bookstore gift card.
I've also cut up the Christmas card to use as an embelishment for another card. I have tons of scrap paper from scrapbooking projects to coordinate with. I've even used some to send as postcards to sweepstakes.
If you aren't a crafter and truly want to do some good with your 2010 Christmas cards, consider www.stjudesranch.org. The children earn money by removing the fronts of the cards to make new ones sold in packages of 10. Last year, the cut off of accepting used Christmas cards was end of February so you might still have some time.