Learned new things there, like:
Free blogs hosted on WordPress.com may sometimes carry Google ads but these ads may only appear if all the following three conditions are met:
1. The visitor is not using Firefox browser.
2. He has logged out of his WordPress account, if he has one.
3. The referring source is not a WordPress powered blog.
What may surprise you is that professional bloggers, or anyone who is making more than $500 per month in advertising revenue from a WordPress blog, also needs to pay a $5 per month fee for the Akismet license.