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I couldn't find, nor am I aware of any 'official' studies aside from The Kinseys Institutes Guide on Sex that claims that although 50-80% or women perform fellatio on their partners only about 35-65% of them derive pleasure from it, the rest are indifferent or don't like it at all. There are a few unofficial folks who have been wondering the same thing. I'll provide some links below.
http://www.thechurning.com/2007/01/09/do-women-like-giving-blowjobs/ (adult content. Be sure to read the comments as they have more of what you're looking for)
Of course there are ways to do your own unofficial research, like http://www.polldaddy.com/ or you can create a blog, or myspace specifically to get people's comments or thoughts about it.
I welcome your thoughts, let me know if you want to talk more.