HT4486: iCloud: My Photo Stream FAQLearn about iCloud: My Photo Stream FAQ
Currently Being ModeratedDec 4, 2012 11:03 AM (in response to Fonarfi)
Your device will keep a rolling collection of 1000 photos in your photo stream album, and photos will only stay in your photo stream for 30 days, after which they are deleted from your photo stream but will remain on your device. See http://support.apple.com/kb/HT4486. This is regardless of the space in your iCloud account as photo stream doesn't use your iCloud account storage.