The reason I haven't made the leap is pretty simple: money and location.
I currently work for a large corporation, making money, and slowly saving, but it's not very fast. I can't support myself for more than a few months before being forced to work again.
So, if I want to do a startup, I need an angel investor to fund me. That brings me to the second problem, I'm tied down into middle america. I love the city I'm in, but it doesn't have the kind of abundance of cash that the coasts have.
So, my plan moving forward is to contribute to open source and personal projects. I'll try to make a few bucks off them, but probably nothing serious. If I hit on an idea that I am really passionate about, I'll work on it more exclusively on the side or whatever day job I have, until it is able to provide decent income by itself.
As far as your ideas question, I have no shortage of ideas, but I have a shortage of ideas that would be good businesses. They are either too small, too hard to monetize, or they are simply that I don't have the passion for them to take them far enough to make them viable.