A couple of quick checks and I have my first ubiquity command written. The best thing I liked about the command was the way you could share it easily on GitHub. You can subscribe to it from here. Interestingly, the rel="commands" tag for ubiquity is automatically added and hence, the subscribe button is present right on the page!
The code itself is not really complex, I ripped most of it from the Twitter example.
The delicious API has a post/update URL that can be used to update, with authentication taken care of automatically. The selected text is added as notes. Currently, there are no tags automatically added. I was looking at a tag could generator, but it seems to be too much of a pain.
I still need the feature to search my web history only, and I am still waiting for infoaxe to add the "import delicious" feature.
In the meanwhile, I am working on a ubiquity command that 'linkifies' selected text with URLs of Google search results; particularly useful while blogging. Watch out this space for more ubiquity commands that I come up with :)