[Ben David Walker](http://bendywalker.com/articles/shared-photo-streams):

> You can store a total of 50,000 photos through Shared Photo Streams (5000 photos per stream, 100 streams), and because Photo Stream doesn’t use your allocated iCloud Storage, you can store all these photos completely free.

When you create a new Shared Stream, keep pressing next to skip the sharing part and your photo will be posted on a private Photo Stream with an incredibly generous limit.

On the side, I’m also experimenting with [Backup to Flickr for iPhoto](http://www.bohelay.org/iphotobackup-en) to see how the new Flickr can work as a private cloud photo storage too.