Yes, you guessed it - our friends at Google did not recognize Memorial Day today. Yahoo did. Dogpile did. Ask did. Live (MSN) didn't but may not do anything special for any day, either. That, I don't know.
Note: you will only be able to see the treatment each of the above gave if you visit their home page today, Memorial Day, May 26. Obviously, if you click over to their page another day, the logos will reflect that day. Google does have this page that shows their various logos through the past several years.
To be fair, Google does recognize Independence Day, and did recognize Veteran's Day 2007.