I have this problem also. It works from iPhone to iPad, but nothing shows up on the Mac. Newest versions of iOS, OS X, and iPhoto. Here's what I've tried:
- make sure photostream is on
- verify that phone and Mac are logged into same iCloud account
- turn it off and on again
- restart phone
- restart computer
- sign out of iCloud on the Mac and sign back in again
- repair permissions
The Mac sees the stream in some sense because I can see some - but not all - of the pics in my finder. But they don't show up in iPhoto at all, and there's no photostream icon in the sidebar. Can't find this issue online except with suggestions to update to the latest iPhoto, which I have. Please help!