Firefox only: Mozilla Labs unveils the first iteration of a natural language web service connector called Ubiquity, a Firefox extension that adds a command panel to any web page. Ubiquity will look familiar to Quicksilver, Launchy or Enso users: you invoke Ubiquity using its key combination on any page and begin to enter your command in the suggest-as-you-type text field. Ubiquity's command set consists of "user-centric mashups" that let you perform tasks using various web services in one place using natural language. For example, you can look up a topic on Wikipedia in-page without switching tabs; you can insert a Google map into a new Gmail message (invoke Ubiquity and type "map [business name] "); you can send a web page to your friend John (hit the Ubiquity key combo and type "email to john"); you can select a paragraph of text in a foreign language and translate it in-page, or map a list of addresses from Craiglist by just selecting them. See these examples and more in practice in the introductory video.
Like Quicksilver's three-paned subject-verb-object expressions, what makes Ubiquity exciting is that it lets humans interact with the web in the natural order we want to do things ("email this to John") instead of making users turn things around and work hard to do a simple task ("must copy this link to clipboard, open new tab, start new email, enter John's address, and paste link into body").
That said, convincing non-power users to hit a key combination to interact with what's essentially a souped-up command line may be a hard sell. But, the command line is indeed making a comeback, and even as an early prototype Ubiquity is a very exciting step in that direction for application launcher lovers. Ubiquity is still an early prototype, but version 0.1 is available for download now from Mozilla Labs.