bill - 12:47 am on Oct 25, 2007 (gmt 0)

From their TOS:

Can I re-publish some of your information on my web site? [qppstudio.net] You are free to re-publish any information posted on this web site, as long as you mention our web site as the source of the information you publish. Any such re-publication should be limited in scope, and serve to illustrate a particular point. To prevent wholesale copying of our published data, some of the most data-intensive and frequently updated pages on this site are protected against electronic copying.

That site is pretty authoritative for holiday/date information. If you want to use their information you have to follow their guidelines. I think a lot of places use this data.