Sure, you can launch. But then what? You still have nothing but time. You can set milestones, and releases. However, since there will never be a "shipped" or "finished" product, many startups end up having no direction.
IMO, software has cycles. Early systems have lot's of known issues that can be quickly fixed. Then mid cycle have little or nothing minor wrong and so you tackle one or more major issues. Then your back to having lot's of little bugs to fix. Microsoft has discovered you can sell both parts of the cycle both new features aka Vista and then bug fixes Windows 7. But, when people talk about the minimum valuable product what they really mean is the smallest cycle where you get something people will pay for at the end.
The secret is to setup your cycles so you make enough money to keep going and or know when to let a product keep without investing in the next cycle. EX: Windows ME. Or Coke with sugar, new Coke with corn syrup, Classic Coca-Cola with corn syrup. http://en.wikipedia.org/wiki/Coca-Cola
Customer Development solves this problem. You have to leave the building and identify real needs among real customers, a real market niche, and to validate your product hypothesis. Then you're not aimless anymore, you're trying to solve a real problem for real people that you've personally met outside the building.
I've never personally met any startup founders that weren't acutely aware of their limited runway. Generally they are haunted by it day and night. People do get aimless - because they don't test their idea in the real market. In a vacuum, its easy to get lost.
