Last month I got a mail from someone who wanted an option to backup all your Google data or just a part of it.
Joe T. sent me an interesting idea: Google Desktop could download your data from Gmail (already does that partially and slowly), Google Calendar, Google Docs, Google Notebook, etc. and make it searchable offline. This way you could use online apps to manage your documents and other data, but still have offline backups that are in sync.
"It's a free service, yes, and as such we are subject to the limitations of Google's whimsy to implement features, whether vital (POP3 download access) or fanciful (assigning pictures to Contact entries). It's no small undertaking, but I'm starting to feel that an ability to bring my data offline, even just as a backup storage base, falls into the good idea-to-vital range."
This may come in handy especially when you read news about Gmail users who lost their emails. Even if Google is not responsible for this, and a Firefox vulnerability caused everything, an easy way to download your data* would have saved the day.
* Note that you can use POP3 to download your Gmail messages. This doesn't include contacts, labels, threads. The feature also has limitations and quirks.