Perhaps I'm not using the search keywords functionality correctly, but in my experience, it works in one of two ways.

- Start typing 'wiki...' and it will autocomplete to http://en.wikipedia.org In order to search that site, I have to left arrow, space, and then type my query. I found that while usually helpful, the autocomplete was occasionally unpredictable/frustrating enough to me that it negated the times it was helpful. Having fine tuned control w/o autocomplete is preferable to me.

- Using the omnibox to enter 'wiki http codes', which will pull up google results. I then have to tab or otherwise use keyboard shortcuts to select the first link, all of which are a worse user experience than the bang syntax to me.