The non-profit Wikimedia Foundation announced that the 'Wikipedia Mobile' application is available for download now from Apple's App Store, and naturally it won't cost you a dime.
At this point, the 1.6 MB open-source application is currently little more than a 'wrapper' for the mobile version of the Wikipedia site, which you can just as easily view in Mobile Safari. Although one advantage to this app is that you can save your search history.
With the current release, the Wikimedia Foundation seems to be concentrating on speed and simplicity. But the organization also seems to be aware of these shortcomings, and I'd expect that, in time, WIkipedia Mobile will become something more full-featured.
In the meantime, you may as well browse through the 100+ Wikipedia applications already available in our App Guide (including the official one) to see which one suits your knowledge needs the best, as it seems the dream of Wikipedia search via spotlight is long off.