I see Photostream as a way of amassing the photographs that come from various sources (iPhone, digital cameras, etc.) into one pool, so that they can then be easily added to libraries. For example, after a recent weekend away, I downloaded all of the photographs on my digital camera into iPhoto on my computer, and was then able to easily add the snaps I'd taken with my iPhone into the same album/event, as they were waiting for me in Photostream. It also meant that I was able to save a few of my favourite pictures, that I'd taken with my digital camera, from Photostream onto my phone's camera roll.
The new Journals thing in the iOS edition of iPhoto, which I presume will be added to the desktop version too, is a reasonable way of sharing photo albums.
But I'm with the OP in that we're still lacking a practical method of syncing libraries. We can collect the photos together in one space with Photostream, share them with Journals, but the current method of syncing is cumbersome (in the case of syncing between iOS and OS X) and incomplete (in that you cannot sync a library between two OS X copies of iPhoto).
The only two solutions I can think of are models were the user has a master library, which is then viewable and editable on other devices, or one where all photographs are hosted on iCloud servers, with changes and additions pushed over the internet between devices. The first one harks to the now supposedly deprecated iTunes-as-a-hub model, whereas the second would presumably place a pretty substantial load on iCloud's storage and data transfer capacities.
A pickle indeed.