I've just tested PhotoStream in Aperture 3.4.5 and i'm searching how to see all my public photostream.
I've check "Photo Stream sharing" in Preferences -> Photo Stream, and they all appears in the menu Photostream.
I've also a Flickr account and albums appears in the menu "Flickr - my name".
May be i can e-mail you a picture of what i see.
I attach four screenshots Yann - one is the project hierarchy - where you'll see PhotoStream appearing in Recent items, but not under the Web section (where you do see Facebook) and the other the preferences pane for PhotoStream in Aperture showing all three boxes checked.
Attachments one and two are from my wife's computer - where she's not seeing shared PhotoStreams.
Attachments three and four are from my computer - we I do see them.
What I notice when I compare these side by side is that there is a difference in the setting panel for photo stream between the two. Mine has a fourth option for shared photo streams - my wife's doesn't.
Yet both s/w versions for Aperture are 3.4.5. There is a difference in what is listed in the Aperture version after the version number, but both computers are fully up to date with no further updates available. (Final two images first my wife's then my s/w version)
Is your view/settings any different?