hmm, I follow a different model which was explained here recently by Des Traynor in a brilliant, short talk:
<a href="http://vimeo.com/81544164" rel="nofollow">http://vimeo.com/81544164</a><p>map any feature in a graph that has people on the x axis and time on the y axis. farther to the right means more users, farther up means more often. concentrate on what most/all users would use most/all of the time. a lot of the other things are noise, added on by other entities, which over time dilutes and destroys your product.<p>you should map existing features as well and kill them off if they do maintain or increase reach and or frequency.<p>of course this is simplified, there is still a lot of balancing and reality wrangling to do, but as a guiding principle it really works. especially when you're getting the "oh come on, let's add this, just a few lines of code" type requests. any add has a long tail, from bugs, to documentation, etc.<p>my 2c.