I agree with the OP on the importance of build quality in the success of pandora, but the other important 'make or break' factor from where I'm standing revolves around the choice of default packages and their configuration in the pand OS.
It been discussed in several threads already although I'm unsure what the devs have got planned OS wise apart from it will be Linux based, which really doesn't mean much other than we know what kernel will be used and there's a wide variety of GUIs that sit atop the Linux kernel, some X11 based some not.
Its generally been agreed that pand needs to ship with both a 'I don't like computers-user', gmenu2x style gui as well as an X11 based gui for doing serious work with and taking advantage of the 1000s of great X apps out there. The gmenu2x style interface needs to be kept simple-as and so shouldn't be a big problem for the devs in producing something that does the job but my concerns lie in how well the X11 environment is put together because if its done well it could have major repercussions for the whole world of computing, giving desktop LInux a big push from the embedded world.
Why? Reason being that this really hasn't been done before. Just like the pdaXii13 x11 OS on the Zaurus, the pandora team can have everything customised specifically for the platform so that everything 'just works' out of the box kinda like OSX on Macs but with more apps included by default (look at how many cool apps Meanie crammed into 250MB for pdaXii13- loads of stuff). Yes, you could install pdaXii13 on a zaurus but it was never sold officially/ pre-installed and you had to have a certain level of geek skill just to install it or even know it existed. On top of that, modern Linux desktop distros such as Mandriva and SUSE have all but obliterated any need for a normal user to ever need to use the command line and Linux really is as easy as, if not easier to use than Windows now. The only problem with Linux on PCs is whether your hardware is supported or not- Linux supports a lot more hardware than vista but as I said already this isn't a problem on pandora- it'll just be a case of how well your peripherals are supported and most will work out-of-the-box.
There's a lot of talk in the tech press now on how Linux is going to take over the budget computing market and Pandora has the chance to be the shining star and the major catalyst. You can't run winxp on the super-power efficient ARM chipsets a lot of these mobile devices use and even if you could it would run like a dog with only 128MB RAM but Linux manages to nip along nicely in these conditions. Seeing as most of the world has never heard of the Zaurus they are unaware that 'pocket desktop' computing is a reality and so the Pandora will be most peoples first exposure to this new computing paradigm- it will also be the first time many use Linux as a 'desktop' OS so everything needs to be made as simple as can be without removing the power and flexibility of the X11 desktop- I'm thinking a kind of combination between Mandriva 2008.1 XFCE and pdaXii13.
I've been testing/using Linux distros and FOSS software for 12 years now and I was one of main bug testers/ idea mongers involved with pdaXii13 so if team pandora needs any help in this respect I'd be happy to package-pick, tweak and test!