I read an article about exactly this by someone who studied the grad school admissions process; it seems many departments are also concerned about the ratio of offers accepted to offers made as a metric of performance.
Looking at previous results, it seems UCSD has sent out rejections before acceptances in the past? Fingers crossed, as I'm still to hear from them and I'm 0:2 with 5 to go.
I applied to 7. I could have opted for lower ranked "safeties" or added unis in cities/departments where I know I wouldn't be happy, but what would the point of that be? If I don't get in somewhere I would actually be happy to go, then there are other cycles. If you have a clear idea of what you want to study, where you would actually attend, and where you could realistically get in, 8 is plenty.
To be fair, I'm pretty sure the Berkeley responses were fake. Nobody has claimed them, some of the notes on the survey seem to target members here, and there are only, what? Three of them?