WordPress.com vs. WordPress.org

Many poeple confuse between this two phrase, WordPress.com and WordPress.org include me. But now I've seen the answer. 
WordPress.com Benefits

• It’s free and much easier to setup
• Everything is taken care of: setup, upgrades, backups, security, etc
• Your blog is on hundreds of servers, so it’s highly unlikely it will go down due to traffic
• Your posts are backed up automatically
• You get extra traffic from blogs of the day and tags
• You can find like-minded bloggers using tag and friend surfer
• Your login is secure (SSL) so no one can get into your account if you use wifi

WordPress.com Cons

• We provide 70+ themes (and adding more every day) which you can modify and edit the CSS, but you cannot run a custom theme*
• You can’t hack the PHP code behind your blog*
• You can’t upload plugins

* The VIP program on WordPress.com for high-traffic and high-profile sites, allows you to run custom themes, custom PHP code, ad code, and WordPress plugins.
WordPress.org Benefits

• Ability to upload themes
• Ability to upload plugins
• Great community
• Complete control to change code if you’re technically minded

WordPress.org Cons

• You need a good web host, which generally costs $7-12 a month, or thousands of dollars per month for a high traffic site
• Requires more technical knowledge to set up and run
• You’re responsible for stopping spam
• You have to handle backups
• You must upgrade the software manually when a new version comes out ( with WordPress 2.7+ there is now an auto-updating mechansim )
• If you get a huge spike in traffic (like Digg or Slashdot) you site will probably go down unless you have a robust hosting setup

The main different is about what they are.

WordPress.org is free blogging software, you can install themes and plugins, run advertisements, edit the database and even modify the PHP source code. WordPress.org is the home of this software. Anyone can download the software for free but it must be installed on a web server before it will work.
WordPress.com is different. You do not have to download software, pay for hosting or manage a web server. When you sign up for a WordPress.com blog, you will get a URL like “andy.wordpress.com” or you can map a domain so your blog is available at “example.com” without the “.wordpress.com” portion.  What you can do on WordPress.com is blog for free.