As expected, Jimmy Wales, founder of the Wikipedia , has launched his search engine, named Wikiseek.com. (This is not a search engine by Wikipedia, but it does use Wikipedia's content - sorry, still catching up). All I have seen are negative reviews about the search engines, you can read Danny's huge analysis at Search Engine Land, his conclusion:
In the end, if you want to search Wikipedia, just go to Wikipedia and search there rather than Wikiseek. That seems the better experience. Or search at Google -- it tends to bring up Wikipedia pages all the time for relevant queries.
I have searched through the various discussion forums and honestly did not find much conversation on it. There is a large thread at WebmasterWorld and a very short one at DigitalPoint Forums.
The overall consensus is that it is currently a poor search experience because of the restrictions of only showing results within the wikiepdia community.
I also did notice someone at WebmasterWorld noted that http://wikiseek.com/ returns a 404, they need to 301 that to the www version.
Forum discussion at WebmasterWorld & DigitalPoint Forums.
Wikiseek logo.

A new search engine that was announced yesterday finds articles and links within the English Wikipedia. Wikiseek, run by a California based startup company called "searchme", is a website which aims to be "A better way to search Wikipedia."

Although most keywords work without problems, Digg users have found search terms that the site does not recognize. If you enter "Chicago" for example, it shows no Wikipedia articles at all, and clicking "Chicago, Illinois" leads to an article on West Chicago, Illinois and other related articles to the subject. Similarly, entering "Christmas", "United States" or "PlayStation 3" only provides links to related articles on Wikipedia, although they are in the top 10 of most viewed articles in the English Wikipedia. Searching "porn" comes up with commercial websites linked from Wikipedia, but not the relevant articles in the free encyclopedia. For most articles however, the relevant Wikipedia article is the first result or among the results.

The site says that "The contents of Wikiseek are restricted to Wikipedia pages and only those sites which are referenced within Wikipedia, making it an authoritative source of information less subject to spam and SEO schemes." The site also offers a Toolbar plugin and a Firefox extension to add a Wikiseek search button inside of Wikipedia pages.

Danny Sullivan at the Search Engine Land blog found Wikiseek's results inferior compared to the  results from established search engines. SearchMe CEO Randy Adams stressed that Wikiseek is still in a beta phase. He pointed out that they welcome feedback more than the average search engine, which can be posted on their company wiki.

Searchme put a button on their main page, encouraging beta testers to instantly promote the site on Digg. In August 2006, Digg had half a million registered users.

Some media outlets have reported that Wikiseek was created by either the Wikimedia Foundation which runs Wikipedia, or private corporation Wikia, which hosts a collection of wiki communities. Both rumors are untrue, says Angela Beesley, co-founder of Wikia and chair of the Advisory Board of the Wikimedia Foundation. "Wikiseek is an independent project with no affiliation with either Wikia or the Wikimedia Foundation."

The Wikiseek site says they contribute the majority of its revenue from advertisement to the Wikimedia Foundation's fundraising effort.