Did Dropbox turn down $800 million from Apple?

Business Insider has reported that multiple second-hand sources informed it that Apple bid as much as $800 million for the file sharing company Dropbox. This seems plausible, given Apple's desire to master cloud computing, and its similar services like iCloud, Airdrop, and iDisk.

However, the sources suggest that Dropbox turned the offer down in order to remain independent. 

Since then, Dropdox has raised venture capital that places the company's valuation at roughly $4 billion. Of course, valuation and cold, hard cash are very different things.