How important is it to have your keyword in a domain for an affiliate marketing website?

Google did away with easy rankings when your keyword is in the URL a while back, I miss those days, but it still can be important if you have the right topic. Check the SERPs (search engine results pages) for your keyword phrase and take note of the results. Are most of them using the keyword phrase in their URLs? If so, then for that particular topic it is still important.