If you click on a link to Coinbase on my blog, and then buy some Bitcoin from them, I may receive a payment from them. I use the Coinbase service myself as once of the places where I purchase Bitcoin, and I also have posted an address on the About page with an address for contributions to help support this blog. That is another way that I am using their services, which I have been happy with.
The current offer is that any reader whom I invite to the Coinbase site using my link, and who purchases $100 worth of Bitcoin or more, will receive an extra $10 worth of Bitcoin for free. Not bad. I will also receive $10 of Bitcoin into my account for this action.