What’s better, multifunctionality or single-purpose? If we refer to digital gadgets and interfaces design there are several good and bad examples for both approaches.
Is there a limit for multifunctionality? The following imaginary design illustrates the problem of multi-function devices and applications: the solution reaches a point where a big amount of features offered block the access to them and makes the whole product unusable or difficult to understand.
An overwhelmed Swiss knife
Multifunctionality could be also a problem in graphical interfaces. In the following picture there is a screenshot of the FStream applicaton for Apple iPhone, an application to listen online radios and other sound streams. This app used to have only 3 visible options at the bottom: Play, Favorites and More. Now it is already showing the option “Record”, which, I assume it is only useful for limited amount of radio listeners. Ohh… it’s so easy to add just one more feature!
FStream App for iPhone
Google Android phones (and iPhones) are a good example of multi-purpose devices. Thanks to their good interface design users are able to manage a huge range of different tasks: music, pictures, work, maps and more. Still, they are victims of their own success; multitasking people could feel the need for more than one phone: users can do several things with them, but not at the same time.
Picture from Google Mobile Blog
Logitech Harmony Remote is a device that remotely controls 225000 different devices, including televisions, DVD players, radios and video games. A real do-it-all device. Unfortunately the interface description on the Logitech website is very vague but if the interface is well done it could eventually be a good product for geeks. But they are not going to sell it to my mother…
The Harmony Remote controls 225000 devices
“Reading is an important activity and deserves a purpose-built device”, said Jeff Bezos to the New York Times. He might be partially right, probably many users don’t want to see more features on the Amazon Kindle. Many think the audio book feature is already redundant (why would you need it if you have a great pocket size iPod?). On the other side, Bezos’ statement might just lack of sincerity; maybe he is not putting more features just because the device is limited by a low resolution, black and white, slow, not touchy screen.
The single purpose Amazon Kindle
Few devices can be more purpose-specific than the WikiReader. Many laughed at it when it was announced, now it’s a top seller. Simple interface design makes it a king in the only thing it does: accessing Wikipedia information without complications. Maybe someone using an iPhone won’t need it but what about children?
The single purpose WikiReader
It is easy to see the symbols on buttons, the contrast is good but having several functions working on one button could be confusing. From Rollei, we liked the way it navigates through pictures (unfortunately I can not show you that).
Having less buttons could make the camera look simple, but this graphic interface show us that this is not always true.
Here we noticed that it is very difficult to see the labels on buttons, the contrast is very bad.
One function for each button could be a good approach. I like the knob to turn the camera on and off, it’s impossible to confuse it with the shooting button.
The “Share” button might have good functionality, but honestly I don’t know what it does. What we discovered interviewing elderly people is that this group avoids pressing on buttons they don’t know what they are for.
This one has some buttons on the top that are almost impossible to see while taking pictures. “BS” seems to be something only Casio uses, we don’t know the meaning.
Painted buttons have great contrast! Unfortunately, it is very difficult to see what’s written on the other ones.
It seems that Casio likes wheels. Unfortunately, these wheels do not behave like real wheels.
There are some contrast issues here (on the buttons), but the most impressive things are the wheels. The one on the top is a real wheel the user can turn, the one on the bottom can not be turned.
These two models (above, below) got a touch screen. This is a risky approach, success depends mostly on how well the graphic interface is designed. For the one below, graving it properly could be quite complicated. 
This model got lots of functionality, buttons and wheels!
Flash position is good here, it’s difficult to place the finger on it.
The wheel could be an issue here and the buttons on top of the camera could not be seen when needed.
Some of the buttons in this camera seem to be part of this brand’s lexicon.
Painted buttons look great but the other ones have very bad contrast, I can imagine this being a big issue using the camera outdoors and even more for the elderly.
I wonder if labels like “AF/AE” are understandable to everybody. Should we carry the manual with us?
On many Canon cameras the wheel looks and works like a wheel, main function of it is to navigate through saved pictures. I like it a lot. 
Interesting design, but using buttons that don’t really look like buttons could be dangerous.
This model goes in the right direction. The wheel is great. Unfortunately the graphic interface is not that simple.
We noticed that symbols on this model are difficult to understand for many people, specially the ones on the top wheel.