Many times people go out to take photos on the street, shooting people as they encounter them. This is called street photography. Street photography can be quite intimidating, mainly because you feel like you're intruding into another person's space. Some people don't want their photo taken. Some people will be rude. It's probably one of the reasons why I don't participate in street photography that often.
The 100 Strangers project is different. First, they only allow one upload to the group site per day, so it's going to take awhile to complete. Second, you have to have their permission to take their photo for this project. In other words, you have to have a dialogue with the person. The purpose it to improve the photographer's skills as a photographer, but also as a communicator.
You're supposed to post a little bit about your experience when you talked with the stranger. Thus far, as of this post, I have posted two stranger photos to my Flicker photostream. I actually missed an opportunity yesterday to photograph a stranger. I had been photographing in an alleyway when I encountered another fellow photographer. We had a very pleasant conversation and it wasn't until after we'd taken our leave of each other that I thought I should have asked to take his photo. I ended up wandering around the village in town just to see if I could bump into him again, but he'd disappeared.
For some of you, this might seem like it would be too daunting, but it really isn't. Think about all the times you end up just having a random conversation with strangers. Many times, it's probably while your waiting in line for something. I can't even count the number of pleasant conversations I've had with people while I was in line for a ride at Disneyland or other amusement park. The same goes for those people that I've met on hikes while out on camping trips.