A great example: It's been discovered that fatty tissue in individuals with obesity often have a very high number of macrophages - white blood cells - that cause a general inflammatory response, in fact a response very similar or identical to what the body would do in the case of a parasite. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC297006/)
It's also well supported that being exposed to allergens at a young age decreases your likelihood of being allergic to them later in life, as the body has time to develop an appropriate immune response while antibody production is still malleable. I.e. A child who has never touched a cat is more likely to be allergic as an adult than one who grew up with cats.
I would argue that the biggest and most effective change that saw an increase in general health and longevity in the 20th century was the widespread use of sanitary cooking and waste management. The ability to stop excrement from contaminating drinking water and food was responsible for a huge reduction in disease and especially spread of parasites.
There's an application that extends usability of trackpad functions on Macbooks running Windows, called Trackpad++ (Link)
Upon downloading for free, it is fully usable, but the owner updates the product with bugfixes and sometimes features once a week. If you don't register the product by sending the owner a donation to receive a license key, it is disabled every week (and doesn't download updates automatically). You can continue using the product, but only if you go online and download the latest version.
This has the benefit of showing off other potential goods you have on your website, giving you free advertising, in addition to forcing users to see the "purchase" button over and over again.
If a consumer doesn't like or need your product, it stops working, no loss. If he wants to test it a little longer, he can keep downloading it, until he decides to purchase or not. When he buys it he is guaranteed updates and a usable product.
Is almost a total disappointment. No camera, no backgrounding, no flash support.
"We shall reach greater and greater platitudes of achievement." -- Richard J. Daley