The Google Custom Search blog just announced a new feature, the Custom Search Results Overlay. What it does is provide a way to have the results of a user's search overlay itself on top of the screen containing the search box. You can see an example of this here.
It's an interesting idea. A bit like a pop-up concept, except it avoids the issues inherent with pop-up blocking. The overlay lets you provide search functionality to your users without losing their focus on your web site. So now you get to provide a better site experience for your users, and you don't have to feel like you are actively driving them away from your web site.