When you activate Akismet plugin, you will be asked to enter WordPress API key. Every user of WordPress.com gets a unique API key they can use to access a number of services. This key should be kept as secret as your password — don’t share it with anybody.
To find your key go to your Dashboard and then click on Users ->Your Profile (or click on your name in the upper right hand corner) and you should see a sentence that says “Your WordPress.com API key is:” followed by a string of 12 letters and numbers. There you have it! You can copy and paste that string to any place where it is asked by Akismet.
For WordPress 2.5.1, you can access your WordPress.com API key by creating account at wordpress. After you login, you can access the WordPress.com API key at your profile.
