Often when building links naturally people misspell the text in the anchor text area. If it happens often enough, you can expect unexpected search term referrals from the search engines. This is the story of a member at SEO Chat forums, the story of an Accidental Discovery.
In a secondary site that I have, I noticed searchers getting in through MSN using the miss spelled phrase: ortgage calculator. So I tried it, and bang! my site (www.mortgagecalculatorsandrates.com) showed up in the first place… Convinced that I must have a spelling mistake on the page, I checked it up and down and couldn’t find it! The other sites all have miss spelings, and yet my site comes up first. The only explanation being that it must be in a back link someplace, though I couldn’t find it. The lesson is: if you are targeting miss spelled words go for the BLs. Now before you get very exited about this one perticular search phrase, let me add that I got 22 visitors in 20 days of September!
Of course there can be other reasons to why this site ranks for ortgage calculator at MSN Search.