L. James wrote the precursor to Fifty Shades of Grey online as fan fiction and self-published it on her own website before Vintage acquired it.

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"By way of comparison, the latest phenomenon in the book trade, Fifty Shades of Grey, sold 664, 000 in its highest week of sales so far, " said David Walter from Nielsen BookScan, which has been monitoring book sales in the UK since 1998.

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The result is far higher than anyone in the industry would have predicted a month ago, but "Mike quickly snowballed into a "Sex and the City"-type release and became a must-see "event" for groups of women in the mood for something other than "Fifty Shades of Grey.

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