Seems like Google, Yahoo, Ask.com and Microsoft Live Search all are not sporting anything exciting or new for Labor Day. They have not done anything special in the past either, so it is not too surprising.
Dogpile is sporting the summer end theme with this:
We, at the Search Engine Roundtable, are also sporting a theme for Labor Day, here is what it looks like if you missed it:
Let's take a fresh look at how search engines respond to the query for [labor day].
Ask.com provides a great smart answer at the top, followed by organic results to various sources on the day. On the right pane are relevant images and news images and articles, plus a link and summary of the Wikipedia article.
Yahoo provides a Yahoo Shortcut with the date for Labor Day.
Google provides just search results and Microsoft Live Search provides some news results for the day.
Forum discussion at Search Engine Roundtable Forums.
