Rick, I'm in Detroit regularly, and the worst thing that's ever happened is a homeless person asked me for my change.
You are right that a mile, let alone a few blocks out can be sketchy in spots... but if you've got half a brain, you dont go there. In recognition of some awesome clean up efforts, parts of the Cass Corridor, which used to be the nearest thing to No-Man's land is cleaned up, and awesome. In fact, I spent a day down there with friends and family over the summer.
As for doing business in downtown, it's honestly been a joy for me. I look forward to going to Detroit. The city has awesome character and I'd like to be a part of the resurgence. Is it going to happen overnight, NO. Are efforts in place to make it an exemplar city, you bet. I'll close by saying Rome wasn't (re)built in a day.