While I get the whole "it's only a sync thing" I find photo stream rather, well, odd that you can't actually view the photos in the stream directly.
And I certainly don't "get" the logic in only showing photo stream photos on a go forward basis. I have had an iPhone 4S for over a week now, and have taken many photos. Well today I finally got iPhoto updated for photo stream on my MB Air and... well no photos from photo stream. Only ones I take from now on. That seems absurd that I can't get photos just because I am only using it now. The photos are on iCloud but I just can't see them on my AIr. Nice. Ugh.
Michael
That's weird. I installed the iCloud control panel for windows on my laptop and it downloaded my entire current photo stream.