I have now browsed ahead to Memorial Day 2006 and see that there are 4 occurrances, two of each of the above variety, one from 12 am - 1am and the other from 1am to 12am.
I found an article in the Microsoft knowledge base that mentioned that (1) Outlook would not do holidays after 2005 and that thay had posted a fix. I didn't download/install anything (unless windows update did it for me).
Any idea what is going on and how I can get back to only one occurance of each holiday showing as an all day event.
By the way, I frequently have an archive pst file attached. could the two attached files be (part of) the problem?