The "nightly experiment" now is something more. Actually I am very surprised to see the amount of stuff I could do with "just" user javascript. It's already beyond my initial thoughts.
So now the plan is to convert it to a widget and get the full widget power, XHR, notifications, sticky preferences, and all that. Then, to complete the Opera version, I would only need to load real Ubiquity command RSS feeds. But that's probably not going to happen anytime soon…
Download Ubiquity for Opera v1.0
The usual warning about the default ubiquity shortcut, CTRL + SPACE, which is used by default in Opera as "homepage" shortcut. You have to remove it, or modify the javascript to assign it another shortcut.
Enjoy!