According to Adam Pash it is important that you save Google managed data as once you lose it you cannot retrieve them back.
"Automatically back up your Gmail account
The easiest way to create a local backup of your Gmail account is probably through POP access with a desktop email client. Since it's completely cross platform and comes with easy Gmail setup baked in, I'd recommend backing up your Gmail account with Thunderbird. If you don't like Thunderbird, feel free to use any other desktop email client for POP back ups.
Back up and sync Google Calendar
If you're looking to back up Google Calendar, the best solution is to set up a complete bi-directional Gcal sync using the cross-platform GCalDaemon. With GCalDaemon, not only can you ensure that you've always got a back up of your latest and greatest Google Calendar appointments and events, but you also get to add, edit, or delete those events from your desktop and watch as they sync back to Gcal. On the other hand, if bi-directional sync is more than you want or need, you can just subscribe to your calendar's iCal feed to back up your events offline.
One other bi-directional back up and sync method I've had luck with in the past involves syncing Gcal via my mobile phone using an application like previously mentioned GcalSync. In order for this method to work well, you need to run GcalSync regularly on your phone andthen also make sure your phone's calendar is set up to sync with your computer when you plug it in. It's definitely the least elegant solution, but it does work.
Download and back up your Google Docs and Spreadsheets
If you've jumped on the online word processing and spreadsheets bandwagon, you've probably already got a lot of docs on Google's servers. Firefox users can back up all or select chunks of Google Docs and Spreadsheet files in various formats (including MS Office or Open Office formats, PDF, plain text, or CSV) in one fell swoop using the Google Docs Download Greasemonkey script.
Back up Google Reader subscriptions
All you need to do is regularly export and save your subscriptions in OPML format (under Settings).
Back up your Blogger blog
Bloggers can easily back up their Blogger accounts using previously mentioned Blogger Backup (Windows only). Just point the program at your blogspot URL and let it do its work.
Back up your photos with Picasa Web Albums
Google's Windows/Linux-only photo application Picasa integrated with Google's Picasa Web Albums a while back, which makes online back ups of your photos a one-click breeze from Picasa. Mac users can integrate similar ease of back up with Picasa Web Albums Exporter or Uploader. The first integrates with iPhoto while Uploader works as a standalone photo uploader."
As reliable as Google and its many services maybe. It always pays if you take a few necessary steps and make a backup of your data so you do not lose vital data at a crucial time like how Om Malik had to learn the hard way.