Robert Young of GigaOm has a great post about social media products trying to be all things to all people. He points out that when Alexander Graham Bell first demonstrated his telephone he pitched it as an entertainment medium designed to deliver music, drama, and news to the people—something known today as radio.
Young notes that while radio and the telephone run along the same continuum of physics they are separate industries and Bell was smart enough not to build a "radiophone." Internally, we have been thinking the same thing about wildly different features of Odeo for a long time but our phrase was "let's not build a boatcar."
While a car that is also a boat and a phone that delivers radio programs are real products—you can technically listen to a phonecast while taking a Duck Tour—Young's concept is sound. It's nice to know what the most obvious use of your product is so you can design for that.
On the other hand, Liz Gannes of GigaOm summarizes a talk by Jawed Karim that explains how YouTube which does huge deals with the entertainment industry really took off when they added features that allow for social interaction between users. Thus, adding some telephone to that radio.
The key seems to be knowing what you are building and adding various features strategically so that rather than conflicting to confuse the product, they work together to provide the service that users want and use. Seems obvious, doesn't it? Well, obviousness is often more elusive than you would think and it's important to find it over and over again every day.