I disagree.
With the exception of very low cost, or free offers that pay you commissions based on very simple actions...
The methods mentioned above are POSSIBLE to use...but it is EXTREMELY difficult to earn a living online as an affiliate without a website of some sort for your promotions. Direct linking in most forms will be a less and less effective manner of making money online as time goes on, in my opinion.
Why?
People seek information on the internet, and a website is a natural part of the information gathering process. If you remove/don't have part of that natural information gathering process, it will be much more challenging to promote affiliate products.
Review sites, blogs, conduit sites, simple HTML sites...all are easy to create nowadays, and domain registration / hosting is SOOOOO cheap and easy to obtain...it almost doesn't make sense not to use a website of some type (depending on what you're promoting).
So, in summary, it seems as though everything in barilj's article here is accurate...but your results may suffer if you don't include a website of some type in your promotions
in addition to your direct linking.
Just my opinion, based on recent testing of course.