"ZotFile...can quickly send PDFs from Zotero to your iPad or other tablet or phone via Dropbox. And then, pull that PDF back into Zotero from your iPad after you’ve finished reading or annotating it. "ZotFile Awesomifies Zotero Attachments". Works with iOS and Android. You can also use it to extract annotations added to a PDF via your tablet, and to automatically rename PDF files, and set it up to automatically add PDFs added to a particular folder on your computer to Zotero via a semi-elaborate automated workflow.

"Manage, annotate, and share your papers on the go." Works with Zotero and Mendeley. It's pretty spiffy.

"ZotFile...can quickly send PDFs from Zotero to your iPad or other tablet or phone via Dropbox. And then, pull that PDF back into Zotero from your iPad after you’ve finished reading or annotating it. " via this 2/13/13 ProfHacker article, ZotFile Awesomifies Zotero Attachments. Works with iOS and Android. You can also use it to extract annotations added to a PDF via your tablet, and to automatically rename PDF files, and set it up to automatically add PDFs added to a particular folder on your computer to Zotero via a semi-elaborate automated workflow.

Accessing Zotero.org directly via your mobile browser. PDFs can be opened and read in PDF erader software (i.e. PDF Expert or IAnnotate) but you can't annotate the PDF and send it back to your Zotero library (however you can do this using the ZotFile plug-in).

Well, so far I have been unable to get this to work on my Android phone, and I don't have access to an Android tablet, but I will update when I have more info...Note comments on the IOS side about how you can use it with other browsers (i.e. Internet Explorer) and on computers you don't own (i.e. doing research at a library where you are using their computers).

A User Guide is available here. Check out this 2011 ProfHacker article on Zandy here. 2/14 update: Has not really been kept up, but is the base for a new Android app.

In beta; a "lite" version is currently available.
I have not tried this yet.

I have not tried this yet.

I have not tried this yet.