You can now get a browser search bar for the open-source Wikia Search engine: Wikia Evolution. A search bar is pretty much a requirement to put an engine in front of users' faces, so this is an expected move by the Wikia Search project. But Wikia Evolution moves the concept into new territory.
See previous review: Wikia Search launches the hackable search engine.
Via the Evolution toolbar, Wikia adds a feature to Google and Yahoo searches: It displays rating stars and an "add" button after each result. Clicking on these links adds info into the Wikia Search index, to refine its searches when you use that engine.
It smells. Wikia's Jimmy Wales makes a big deal about how his rating system and open engine are superior to closed systems like Google. Yet this tool asks users to rate Google's own results in order to improve Wikia's. It works, and it's a very clever way to build on the work of others, but it essentially appropriates Google's crawler results for another engine.
I admit this argument would hold more weight if Google and Yahoo allowed users to rate search results. But I believe that eventually they will (beyond current limited experiments), and then we'll have another problem: feedback confusion. How will users determine which service they are rating a result for when they decide to provide feedback?
Mashing sites and content together is the grist for a lot of Web innovation. But taking results from one service and building a direct competitor out of them is not quite kosher, in my book.
Another example of this is Twinkle, which is building its own social network, in part on Twitter; if you to use the Twinkle iPhone app as a Twitter client, you must also get a Twinkle account. And as much as I like it, I feel FriendFeed also skims the cream off the top of the networks that feed it (again, Twitter, but also blogs).
As in evolution, parasites can, over time, strengthen their hosts--or lead to very interesting and robust cooperatives. But they do run the risk of being squashed before they do very much.
(By the way, Wikia Search is really improving. I'm not using the Evolution toolbar, but I have added Wikia Search as an option to my Firefox drop-down list of search boxes. I like it.)