One of my apartment-mates back in grad school was an immunologist. She told me once about the first rule of public health: it's only a cure if people will actually do it, or use it. For example, abstinence is not an effective way to prevent HIV/AIDS, or teenage pregnancy, because in practice, people won't abstain.
I've thought about the difference between "works in the lab" and "works in the field" many times in the context of software engineering. Take the idea of doing rigorous up-front design using UML, for example; it sounds good, but I don't know anyone who actually does it day-to-day, so I don't count it as a "solution". In contrast, while purists may sneer at test-driven development (TDD) as "hacking to solve hacking's problems", a growing number of people actually do it.
Which brings us to Future Email, a new web service that'll send you messages at specified times to remind you to do things. We all use email as a to-do list to some extent; half of the messages in my inbox right now are things I'm supposed to take care of. But since it's easy to overlook things that have been lying around for a while, Ben Sinclair has come up with the idea of pinging people when they most need the reminder. Simple, and a good fit for the way we actually work.