How quickly do you mail thank-you letters to donors?

The book, Donor-Centered Fundraising, did a national survey of donors. The results said that donors expect a thank-you letter within two weeks, although a few days is even better. Major gift donors expected a response, preferably a phone call, within 24 hours of making a major gift. How does your non-profit stack up? How can you streamline your gift processing process to get thank-you letters out quicker? What's standing in your way?