Yes its True
You can use Dropbox as free CDN for your WordPress blog

What is CDN ?
CDN is contain Delivery system  which will basically  speedup your web site loading time You can read more details here 

What is Dropbox ?
Dropbox is file hosing and file sharing service, it provide 2gb instance data with you signup for see here

To setup Dropbox as CDN follow this steps

• 1) Install wordpress plugin Dropbox CDN and active it
• 2) go to Public folder of your dropbox account and create one public folder with and name I have added as CDN

• 3) know you need to go to cpanel of your host copy wp-content to dropbox.
  to to that to to file manager locate wp-content and compress that folder and download it and extract that folder in dropbox
• 4) know you need to copy url of of any file which is in the dropbox cdn folder and past it in the plugin

now you can feel the your web loading speed got enhanced