First, note that I'm not primarily a sci-tech researcher; I've been a business researcher almost all my adult life. That said, WorldWideScience.org sure is cool. It offers a one-stop metasearch in 50 national science portals, ranging from the Indian
Academy of Sciences to Science.gov, Canada Institute for Scientific &
Technical Info, CERN, and a host of others. I find this an easy first stop when I'm looking into something I suspect would be in the public literature, searching for something that I think a government agency is likely to have studied, or trying to identify the leading voices in a field.
Yeah, it's not perfect. Its advanced search option isn't advanced; since it's a metasearch engine, it dumbs down each query to the lowest common denominator. There's no way to limit your search to only free sources and yes, a good amount of the content in WorldWideScience isn't free. When you click through on a title, you're dropped immediately into that database. If that file is hosted in a non-English speaking country, you may have trouble using the interface.
That said, their search results screen gladdens my heart. There's clustering on the left, sorting and limiting features, and the ability to export the citations. It also shows how many results you got from each of the portals, which might prompt you to go straight to that portal and search it directly.