We're increasingly using cloud-based tools for work and communication  such as Twitter, Facebook, Google Docs, Microsoft Office Live, Tumblr,  Wordpress, Blogger, Posterous, Flickr, Picasa, and on and on.
The data from those online tools could be erased by some software bugs. So you should save those data from these bugs.
            But that doesn't mean you should forego a solid back-up plan for all  your online data. If the worst ever does happen, and a free Web service  dumps your stuff permanently, the only response you can reasonably  expect from these companies is: "oops, sorry."
            With that in mind here are a few suggestions on how to add an extra layer of security in case the cloud lets you down one day.
Gmail and Friends

The  easiest way to create a local back up of your e-mail is to use a basic  POP3/IMAP e-mail client such as Mozilla Thunderbird, Apple's Mail app,  or Windows Live Mail.  If you don't like using an e-mail client for  daily use and prefer to use the Web interface instead, just fire up your  desktop program on a regular schedule.  Even if you launch your desktop  client once a month, you will at least have the bulk of your mail  stored offline.
Facebook

Facebook  recently launched a handy feature that lets you export almost all of  your Facebook data into a handy ZIP file.  All you have to do is visit Facebook's export tool  and click the download button.  Then you'll get an e-mail when your  file is ready to download to your desktop.  This is an ideal task to do  once a month or even once every season.  You don't want to lose all  those mobile uploads should the worst happen, and it makes it much  easier to move your data around should you wish to leave Facebook one  day.
Blogging

The  best way to save all the hard work you put into your blog posts is to  save them on your hard drive before posting them to the cloud.  Many  blog writing programs are compatible with the most popular blogging  platforms such as Blogger, Wordpress, or Tumblr.  Mac users can use a  blog writing program such as MarsEdit ($39.95), which saves a back-up of every blog post you write using the app.  For Windows users, Microsoft's free Windows Live Writer  will save your posts written using the program to a file in your  Documents folder called "My Weblog Posts."  Most blog services also have  an export feature to download all the posts you've already written.
Twitter

You could subscribe to your own Twitter feed using a desktop RSS reader such as NetNewsWire for Mac or FeedDemon for Windows. But most desktop programs limit how many items you can download via RSS.  Another option is to try a free service such as TweetBackup and Tweet Scan Backup,  which let you grab your past tweets and export them to your desktop.  Keep in mind these services can only grab a chunk of your most recent  tweets (Tweet Scan Backup only grabs 1000).  If you tweet more than that  or are coming close to that limit, make sure you back it up before all  your 140-character witticisms are inaccessible.
Backing-up your data may be a pain, but if you want to maintain  control while still enjoying Web-based services you owe it to yourself  to back up your stuff locally.