[antiuniverse]

It allows you to upload PDF or website snapshots, and by default an account is granted 300 MB free storage. They also have paid upgrades:

2 GB: $20/yr 6 GB: $60/yr Unlimited: $120/yr

I've had the paid 2 GB plan for a while, I've got about 800 MB stored with them, and I've been very happy with the service.

Between the Firefox connector, the automated PDF OCR metadata lookup, and the ability to pull in metadata from DOIs, Zotero makes indexing things insanely easy. It's like MusicBrainz for articles. I'm always surprised how many obscure PDFs it correctly recognizes and indexes for me.

[lou1306]

Personally, I just sync metadata and use my institutional Google Cloud storage for PDFs. A little more convoluted (I think this wouldn't work without the ZotFile plugin) but it appears to work across my 2 devices.