Well, the product is still around. It's just not called "Citrix Streaming Server." Now it's called "The application streaming feature of Citrix Presentation Server 4.5, Enterprise Edition." (How's that for a true-but-misleading title?)
This little gem came to light in an email exchange with one of the Citrix Streaming Server Feature team members Manu Chauhan, one of the guys I interviewed for a Brian Madden Live! show when I visited Ft. Lauderdale last December.
Here's the story: Ruben Spruijt is giving a session at BriForum in a few weeks called "Streaming Smackdown." It's a head-to-head comparison between the Citrix Presentation Server streaming functionality, Microsoft Softgrid, Altiris SVS, and Thinstall. As part of this presentation, Ruben is making this super-cool gigantic feature matrix that shows which products have which features, and he's sharing a draft version of this matrix with each of the vendors to ensure that he doesn't miss anything. (Of course he's not blindly accepting all of the comments that the vendors are making, but he's taking them all into consideration so that he can provide the most accurate yet independent picture to the BriForum attendees.) We'll make this chart available on BrianMadden.com after BriForum as well.
So anyway, as part of this process, Manu shared Citrix's feedback on the draft of the matrix. As part of that, he provided the insight that before Presentation Server 4.5 was released, Citrix were planning on selling the streaming functionality as its own product to be named "Citrix Streaming Server." But since they ultimately decided that the streaming functionality would only be available as part of CPS, it's now just the feature of CPS instead of being called CSS. Make sense?