This is probably one of the best articles on cacao and cocoa butter content I have recently come across. There is a lot of marketing noise on cacao percentages.

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Just a glance at the premium chocolate bars on display at any gourmet market will reflect the trend to prominently display cacao or cocoa butter content on the chocolate labeling.
The author is correct. The higher numbers do not reflect the best taste. Like wine and coffee, the origin and processing of the bean plays more of a factor in taste and quality than the percentages of cacao. Take the Single Bean Grand Cru Maracaibo as an example. It is without a doubt the finest chocolate I have ever placed in my mouth. The rich finish is without doubt the result of it origin and processing.

For the article I mentioned on "Cacao In Your Cocoa?" - A Chocolate Primer" , the complete text can be found on the courant.com web site.