Although I like the minimal setup i.e. just a bookmarklet, I don't see why I would ever use this over ubiquity. Perhaps browser-independence? If that's your thing, I'd recommend
http://queri.ac which has plenty more features:
* users can subscribe to public commands
* commands have optional query history
* public user, command, query pages
* command tagging
* commands have a powerful set of options, just like in a commandline, which map to url parameters: http://queri.ac/options_tutorial
For more sites that have been doing web commands for years: http://delicious.com/tag/site:type=cmd