Are you familiar with FreshDirect? It's an incredibly popular (and profitable) service for grocery delivery in NYC. As the article mentions-- in big cities, this is a viable business.
I think the point that a lot of you have said-- essentially, "so what if you fail? You can find another job" -- really resonates with me.
I'm leaning towards doing this now because I have no kids or mortgage at this point. I really appreciate all the good responses in this thread. It's definitely a scary, but exciting, time as we consider it.
The one other factor is the drop in total income. The hope is that's temporary though-- our goal is that more time spent building the business will pay off in spades.
There's something about getting the support of people who have been in similar situations that helps with this kind of thing. Even online here, it's reassuring. So thank you all again for that.