Jelly Bean will be phone and tablet. We will most likely not get it officially, although it is possible. We will, however, be one of the first to get it unofficially either way, and i can just about guarantee this.
I don't think the nexus s will ever see "jelly bean" or any newer versions officially.
The way it typically goes, our nexus devices are flagship phones, and then receive one more update as the next nexus comes out, then become old news. Kinda sad, I mean even the first sense phone, HTC hero, is getting ice cream sandwich ports. I guess carriers and google just dont want to spend the time to support a ton of devices.
I don't think official Jelly Bean will reach Nexus S. Nexus One also has 1GHz processor and 512MB RAM like Nexus S and it didn't get ICS from Google although in theory it could normally run it (if Galaxy Mini can run ICS ROM Nexus One can run official version, it's just that Google doesn't want you to buy that old stuff, they want you to buy their newest flagship). So I believe it's 2 latest devices only, which means Galaxy Nexus and the next Nexus device will get Jelly Bean, NS - I doubt it. However there are always ROMs
Btw, I read that JB should also expand to desktops and laptops, it this true?