I'm sorry, but I'm really not interested in yet ANOTHER todo app/website/whatever. Please come up with something innovating. Creating the millionth TODO app and calling it a 'startup' is just not going to work. We have enough of these things. There's no need for it, and it certainly shouldn't be called a business, because it simply isn't. (the same goes for the thousands of project management apps, hour tracker apps,…
Build something that attacks a clear need, has clear competition, and comes at the market from a slightly different angle and you can oftentimes build a huge business just by executing well. Trello? Asana? Sprint.ly? All doing REALLY WELL. I know a couple of guys who built "twitter sentiment tools" recently. They launched into a crowded market of people doing the same thing. They're now nearly 30 people strong and are doing millions in revenue per year. In big and/or growing markets, there's nearly infinite opportunity.