I've been using this in beta for quite a while. The PDF reader is really very good, and I love the fact that my highlights and notes are not added to the actual PDF file. (I don't want to mess up the original PDF file, because I like to keep those files in pristine form so that e.g. I can share them with students.)
Some people here are asking about paying for storage for the PDFs. My solution to this is to store my PDFs using Dropbox, and to use links in Zotero. That way, even if I give up on Zotero, I still have the files. And I already pay for Dropbox, and just don't want one more bill to pay.
And, woohoo, an iOS app! That's very sweet.