Social Media Examiner had a great blog post the other day about the FTC regulations regarding disclosure when you post endorsements and testimonials in social media. The post explains nicely what the definitions are for : connections, endorser as well as what full disclosure means and the penalties for non-compliance.
Essentially you need to make certain that you are letting readers and visitors know if you were paid to promote to product, or given the product free to try or have some connection to the company offering the product or service. If you are promoting a product as an affiliate, you can simply let readers know this as well. Some sites or newsletters I have seen also indicate that affiliate or not, they love the product or service and would still promote it.
I encourage anyone blogging or using social media to read the FTC information and be clear on letting your website visitors and online connections know why you are mentioning or promoting the services and products.