I haven't noticed it before, but you can add an as_qdr parameter to the end of a URL in Google to get a drop-down menu (next to the search box) that lets you search by date. For example:
http://www.google.com/search?&q=macosxhints&as_qdr=d
So I wrote this bookmarklet that does that automatically:
javascript:window.open(document.URL + "&as_qdr=d")
You can customize it as you please:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080429200543638