On its own, this doesn't sound very exciting: building a mini web app in JS sounds a bit dull, but then add in capabilities to access local storage, specialist hardware such as accelerometers, your call log and networking capability and what you'll end up with is a very powerful development environment. The range of applications that can be deployed with this is quite broad.
There is, however, a problem: Apple have beat them to it. However, with Apple, you need to learn Objective C. I was thinking about writing an iPhone app a little while ago but this completely put me off; maybe instead I should develop a Widget? It doesn't appear that the reach or complexity of this technology is good enough yet, but time will tell and hopefully adoption of this platform will be quite broad.
One thing that would make things very, very cool would be for the Atlas technology, demo'ed yesterday, to be able to create widgets. If that were the case then you'd have a very, very fast way to deploy mobile applications. I have a feeling it would work, but without access to the technology, I won't be able to tell - well, not until November 5th anyway. Watch this space?