I know what you are thinking because I made the same mistake: no, this is not Jimbo Wales's putative Wikia search engine. Wikiseek comes from Searchme, an entirely different company, and it does something entirely different. What it does is search Wikipedia and any pages that Wikipedia links to. Pages, not sites. This might be useful, if you use Wikipedia a lot. It costs nothing to try.
If you want more info, Search Engine Land has a huge article about Wikiseek, which includes comparison searches. It's generally pretty negative, but Randy Adams, CEO of Searchme, responds: "As a small start-up facing the daunting task of writing a large scale search engine from scratch, we don't expect to get it right the first time!"
The major limitation is that Wikiseek can be no better than Wikipedia in providing a comprehensive to guide to everything of interest on the web. The advantage is that, unlike Google, it doesn't contain hundreds of millions of pages of spam, though some does slip through....
