Evan Williams former CEO of Pyra Labs/Blogger has a nice little list: 10 Rules For Web Startups.
#9 from the list is my favorite:
#9: Be Agile
You know that old saw about a plane flying from California to Hawaii being off course 99% of the time, but constantly correcting? The same is true of successful startups except they may start out heading toward Alaska. Many dot-com bubble companies that died could have eventually been successful had they been able to adjust and change their plans instead of running as fast as they could until they burned out, based on their initial assumptions. Pyra was started to build a project-management app, not Blogger. Flickr’s company was building a game. Ebay was going to sell auction software. Initial assumptions are almost always wrong. That’s why the waterfall approach to building software is obsolete in favor agile techniques. The same philosophy should be applied to building a company.
Sounds like a good plan to me :)