Paul Graham once suggested that startups pose their mission statement as a question. Google's question might have been "Will the PageRank algorithm deliver results that are so good that they lure users away from Altavista?"
My great lesson from my travel app is that the key question was not "Can you build a decent iPhone app quickly and cost-effectively?" but "Will people look for an app to help their specific travel experience?"
The answer, right now, appears to be "no."