What makes an application go supercritical ?

When Mark Shuttleworth talks about his thoughts of building up an Open Source application, it reminded me of a previous similar experience. My own experience is really that one can fall very easily into the problem of having a technical solution/framework/language running the functional requirements. What happens is that one waits so long for some features to be implemented that the developer feels that he/she has invested too much that she/he cannot turn back. The longer the time people wait for a functionality to show up, the longer the developer is cornered into the framework/language he/she has already used. In the end, the list of needed functionalities builds up and the user's interest winds down. It is therefore all the more important to have both a person involved in the day-to-day use of this application be the project manager and have developers use a language/framework that is responsive to the speed at which the project manager and other alpha-users can produce new functionality requirements. In our case, the initial use of Java brought the former item to light, we had to switch to PHP. Evidently, the ideal case would be to have a developer on the end of the line of a call center a la Paul Graham ( check for "while the user was still on the phone"). Lisp anybody ?