The big thing holding the Atom back is the chipset. Most people I know will not buy Nvidia, since they are a low quality maker (compared to Intel) and have a lot more problems than Intel does with their products. Nvidia offers interesting things, but also headaches and aggravation.
But, Intel makes a terrible chipset, so you're in a situation where you either buy a crap chipset, or buy a chipset with good features from a crap company. Who wants this choice?
So, I'm personally waiting for a decent all Intel solution. I'd buy an Intel/ATI solution too, but there is nothing like that, but Nvidia is not a company I will buy from. I am not alone in this, most of the people I work with and know won't buy Nvidia. Well, not most, but probably close to half. So, for that reason it's relevant.
Also, the Ion doesn't address the real issues with the Atom platform, which is the processor. I mean, it can help in some situations, but, really, it's up to Intel to increase the performance of the processor to really help make this platform more useful.
So, I think this is much more significant than the Ion. You get better performance in every field, and you don't have to buy Nvidia products and potentially have problems. Even if you don't, you can't compare the support from a company like Intel, to a half-rate company like Nvidia that releases software that regularly gives BSoD (Ntune, anyone)?
Now, before everyone yells at me at how good Nvidia is, you may believe that, and many people do, but there are also many that do not. A buddy of mine bought a Core 2 motherboard with an Nvidia chipset, after me warning him not to even think about it. Of course, he knew better, and I was just being ridiculous. Two days ago, he messages me about problems he's trying to solve, and then does some research and finds all the issues about his 790i chipset, after blowing up with Ntune and finding out that's a common problem. Of course, after I berated him for his insolence for not listening to me (you'd do the same thing, we're all human and love gloating), he was funny and claimed his motherboard was fun, and just needed tweaking here and there to make it stable. Of course, this is after reading page after page of 790i issues people have.
So, buy Nvidia if you want. It's got the additional feature that you'll be able to post on more forums about the problems you have with it, and be able to share with fellow users. That's nice really.