I really don't understand all the confusion over API keys. It's just not that freakin' difficult.
1. You go to http://wordpress.com/signup and create a new wordpress.com account. If you already have an account with wordpress.com, just login on http://wordpress.com and skip this step.
2. After you've created your account and verified your email and such, you should get an API key in the second email. If you don't, then you can go here: http://dashboard.wordpress.com/wp-admin/profile.php and login and there's a line of text that reads:
Your WordPress.com API key is: APIKEYHERE. Don't share your API key, it's like a password..
3. Copy and paste that key onto your own blog where it asks for it.
It's really not that difficult. Just remember that WordPress.com and your copy of WordPress on your own site are two different things, even though they may look similar.
You only ever have to do this once. That API key works with both Akismet and the Blog Stats plugin and whatever else they come up with in the future.