Can an HTML5 application that is running in a browser access native resources. The application would possibly be online or offline at any particular time.
For the sake of a specific example could javascript in the app access the camera and take a photo?
For this to be a viable option the answer would have to be yes for iphone and android.
Accelerometer and camera, currently (2011-01-08) no. Notifications, partially. GPS can be accessed with the
window.geolocationobject.A product like PhoneGap allows almost full native access. It takes your HTML/Javascript apps, adds some hooks, and compiles to native for Android, iPhone and a few others.
There are also some hacks that install a tiny native iPhone app to do the camera access: iphone-photo-picker. Your web app can make a call to this app using a special URL. When finished it returns to your app.