A meta-search engine is a web searcher that sends your inquiry to Google and to other search engines, rather than searching its own database. This review at a "search engine optimization" site (which basically means they're more concerned with results placement than doing effective research, but still they know their search engines) takes the view that meta-search engines aren't really all that much better than Google. I generally use them only when I have a very specific inquiry with a lot of search terms. (For some reason this review don't consider AllPlus, although it may not be any better.)
The review did tell me something I didn't know before, though -- there's a meta-search engine, FuzzFind, that includes Delicious in its search. Delicious is a social bookmarking site. Social bookmarking means that instead of (or in addition to) website bookmarks that are stored on one's own PC, people can store them online, in a central location. This creates a sort of recommendation system -- if more people have bookmarked site A than site B, you might want to look at site A first. It's a basically another way to get some kind of indication of quality in a results search, so it's great to see that included in a meta-search engine.
Give it a try and let us know what you think!