A full working version has been around since last December and it can be found in canvas form here and here's how it looks like once it's installed to a page.
It's all wrapped up in CodeIgniter awesomeness but it's actually quite small, and can easily exist outside of a framework.
But it doesn't. Because structure and discipline, man!
Anyway. Page Search works well for pages with a small number of posts and it does not break for pages with tons of posts but since it only searches within a particular time frame, the user is required to keep pressing the Older Posts button until it either finds a match or it doesn't, in which case it will say so.