I think taking the photo then showing it to the person (or, in the case of film aficionados, telling about it) is an acceptable compromise. On contract, I always ask first. But sometimes . . . the moment slips past you if you wait and ask.
It's one tough judgement call after another. My two primary concerns in street photography are representation and reputation. I ask myself, Have I fairly represented the subject? His or her feelings? If/when the subject sees the still, will s/he love it? Hate it? At the same time, you may have an artistic responsibility to convey the 'ugly' side of the human condition: poverty, bereavement, prejudice, violence. . . and that's not a side most people want others to see. Heck, most people won't let me take their photo this season due to runny noses. So then it comes down to reputation. Yours. Mine. If you're working in your home city, chances are you'll run into that person again some day. Once you've lost your credibility, it's next to impossible to get it back. You might get a knuckle sandwich.
Okay, okay, the numbered list.
1. As a general rule, ask people before you take their picture. I know that awareness of the photographer and the camera changes the image. You know that, too. You should still ask whenever possible. Some people don't like having their picture Out There. Some people have religious, cultural, and or personal reasons which prohibit images of themselves being taken. Respect that.
2. When you can't ask the subject, ask yourself if the shot is worth it. I mean, if something is so beautiful it strikes your heart like Stendahl, take the freaking picture. No matter what. Just be ready for any eventuality if you're taking a picture of someone's ugly side. Insurance on your camera might be a good idea.
- Street photography tips from the Digital Grin Photography Forum.
- Discussion thread on Flickr, mostly the candid/photog incognito approach.
- Mixed bag of photo tips from National Geographic.
- General commentary on street photography via photo.net.
- A digression into street photography ethics from Stephen Haynes' blog