They are the newest thing in the world of coffee, and their speed and convenience is slowly but surely winning people over to the whole idea of brewing just one cup at a time. The big question people always have is whether or not they want to sit and wait for each and every cup. Once you know how the machine works, you'll stop worrying.
The secret is the added pressure. A drip coffee maker is slow because you have to sit and wait for water to slowly drip through your coffee grounds to produce a pot of coffee. A single serve coffee maker heats the water very quickly, then forces it through your coffee grounds under pressure (similar to an espresso machine). This means you can brew up one cup of coffee in just a minute or two (or less).
Compared to the passive drip system, a single-serve machine is usually a little louder because it has a pump system that runs with every brew cycle.
Because each brew is designed to produce just one cup, you need to be pretty precise in how you portion out the grounds. That's why these machines all take pre-made "pods", though some manufacturers have different names for them. For Tassimo, you use T-discs and Keurig uses K-cups for example.
When using your single-cup machine, all you really need to do is insert your particular type of pod and let the machine brew. Whether or not you need to adjust volume or time settings will depend on your machine, but it's usually just a button or two to deal with. The boiler heats up almost instantly and forces hot water through your pod. You usually will have a hot cup of fresh coffee in under a minute. They are incredibly easy to use even though they may seem more sophisticated than you're used to.
After your coffee is brewed, you have to remove the used pod and dispose of it. Some types of pods could be reused (like the type for the Senseo) if you really wanted to squeeze a second cup out of it, but most other types can only be used once because they get punctured during brewing.
Another somewhat unique feature of the single-serve coffee maker is that you can use it to make drinks other than coffee. Since your ingredients are already packaged up in a pod, you can easily use the same machine to make different kinds of tea and some models will even make hot chocolate.
All the grounds (or tea leaves) are kept inside the pod, so there is no mess to clean up when you are done. Just pop the used pod out and throw it away.
Basically the entire function of these machines is that you insert the right pod (coffee, tea, hot cocoa ...), let it brew, and then take the used pod out. That's all you need to know, and you'll have hot fresh coffee with every cup.
