I can answer this. I'm a paying Dropbox customer and I didn't donate my data. The information is mine, and we can discuss using it, but my expectation of privacy includes Dropbox not using it for any purpose that isn't storing and serving it to me unless I've expressly stated otherwise.

While I'm not that interesting of a person, I do have an interest in things like my tax returns, financials, and other PII to not be in the hands of Dropbox employees.

Short answer: Dropbox is doing the right thing, and I really appreciate that.