Also, when you install the SDK, there is an optional component you can install for each SDK version which includes demo apps. These demo apps are very instructive and useful to study, and can serve as a starting point for your own app.
Eric Schmidt has stated that he thinks the majority of mobile apps will be developed using Web technologies within 2 years. That's probably not unreasonable given the continual increase in richness of the HTML5 JS APIs and the benefits of cross-platform apps. In case anybody is looking to go the HTML5 route for their Android app this weekend, see this advice from Google on developing HTML5 apps for mobile:
Note that you can now remotely debug Android Web apps over USB using the Chrome Developer Tools on your desktop machine (kind of like using Eclipse on your desktop to debug Dalvik apps over the wire) -- very cool: