I built a search plugin for this very reason, but of course like Matt said, you can't control a lot of things on the user's site, so my plugin doesn't work well on shared hosting for larger sites.

Something I built into my plugin, and would want to see available in a future solution, would be some ability for it to take into consideration the actual markup/output used for the content. This way, it could automatically build relevancy on specific keywords per page and take into account other content on that page which may not strictly be in post_content or the title. Display of custom fields is also important, because it's not jus the data, there could be templating stuff that is essentially invisible to plugins that only look at meta.

Anyways, I don't have a ton of time to work on my search plugin any more, I'm focusing on Pods mostly. But I know that when I get some more time, I'll be looking into a few more updates, but I hope a better solution comes out so I don't have to spread myself too thin.