Now this is something that looks really useful. A PDF Search engine.

Now, you might think that that isn't all that useful but it is. For there's a huge set of documents that are not really well served by the current search engines: those that are in the .pdf format. So an engine which only looks for those and allows you to find them is indede useful. Think of all those manuals, textbooks and guides which are in this format. Finally you're able to find them in a useful manner.

With the traditional engines you're forced to hope that someone has labelled them properly: now you just don't have to worry about that.