At the time of writing, if you do any of these searches on google:
...you'll notice two patterns:
I noticed this because these are referals from my logs that I've backtracked and listed. In all cases it's unintentional misspellings either by myself or people commenting within the pages. If it wasn't for these "double misstakes" certain people who never have reached my site. You can't control how bad people spell (especially when it comes to names) but you can control your own content.
In the case of 7 wounders of the world I could have delberately included a spelling misstake of "wounders" to catch both those who can spell and those who can't, thus increasing your reach via Google.
Personally I think you should, as a web master/content developer, avoid as many misspellings as possible and not try any cheap tricks but perhaps in some extreme cases, this phenomena can turn to your own advantage. Interesting.