With more and more work being done "in the cloud" with web-based applications that store data on a remote server, edited through a web browser (or specialized client application), you'll want to backup the remote data locally.
The way to do this is to export the data using a tool that automates the process. For example, Google Docs Backup.
One of the nice things about Application Service Providers is that they save you from installing and updating software. The big risk is that they'll upgrade and leave your older documents unusable.
Legacy data in traditional backup scenarios is managed in two ways: one is pickling, where an entire system and software stack is retained to read the data. Another way to manage legacy data is to convert it to newer, more useful formats, or to older generic formats.
Cloud computing leaves you only the latter option. So, applications like Google Docs Backup try to convert the data to something generic.