Guess we have to withhold judgment until we see the range of control(s) we have over PotoStream!
That updated description (from erijkgabriel link) certainly implies that if I come in from a trip and dump a couple of thousand NEW photos, those get pumped to PS, wiping out everything that's out there with all those new, but not yet screened, edited photos from the most recent shoot. Oh -- and since you can't edit or delete "the stream", heaven help us when embarrassing shots just get pumped through before we can delete or move to private storage locations.
Hopefully, Aperture will allow us to control what gets pushed to PS from a camera import!! I guarantee that not every picture is ready for public viewing or sharing across all household devices immediately after being shot!!!!
Then again, I'm caught in that same vicious implementation chain of dependencies Apple has imposed on us. Can't turn on iCloud until I turn off MobileMe and I can't do that until I figure out what to do with the thousands of photos I've got in MobileMe galleries and iWeb sites (mine and kids and grandkids sites)...via Aperture and iPhoto.
I'm a huge Apple proponent, our entire home is Apple, our kids and grandkids have "been converted" to Apple users, but this arbitrary elimination of Gallery functionality is making me crazy with frustration and outrage.
I look forward to reading more about how iCloud allows for controls of what gets pushed, when and under what conditions. For privacy, security, creativity and just plain old efficiency, that strikes me as a fundamental set of requirements.