Our class roster contains a Class size meter. The code to visualize class size using a meter is not part of the Google spreadsheet application. It was added by another programmer who may or may not have worked for Google.
This is possible because Google (like most other network application companies) has exposed an application programming interface (API) to Spreadsheets. This makes it possible for a programmer to create visualizations like our class meter, which all other users can include in their spreadsheets. Google hopes to create a developer community around this platform. If successful, they will enjoy network effects -- the more developers, the more valuable the application becomes.
To facilitate the growth of the developer community, Google provides threaded discussion forums like this where developers can ask questions and help each other out. Google will assign a few employees to join and participate in this group. This gives them feedback on what the developer community is saying and trying to do. Questions may be answered by the Google employees or members of the developer community at large. Google also supports the developer community with tools like this.
These community-building sites are an important part of the application.
The second page of our roster shows a map of student addresses. Note that it is a live version of Google Maps, not a static image. This is possible because Google Maps also exposes an API. Applications like this, which combine two or more services are called mashups.