I've lived my entire sentient life with a cable or faster Internet connection. I spend virtually all of my time that is not spent going out with friends, eating lunch with colleagues, or having alone time with my partner on my laptop, Xbox, or Nexus S. I am, seemingly, what you fear.
I cannot think of a single reason why it would be more productive for me to talk to a homeless person instead of doing any of the things I do on computing devices on a daily basis. I don't think you can name any, beyond straw men like "you're wasting your time looking at pictures of coffee cups on the Internet." Because my life is constantly mediated by technology, I can tell you with very good precision that of the 8,760 hours in 2011, I only wasted 939 of them (and most of that was playing video games over the summer -- it's arguable that I'm not wasting time by experiencing the story of Mass Effect the same way I wouldn't be wasting my time experiencing the story of The Hunger Games, but books are more high status, so I'll give myself incentive to prefer them over video games).
If uploading pictures of coffee cups to the Internet is what you do with most of your time on computers, I feel genuinely sorry for you, and I hope that you can find a better hobby. I don't think that talking to random people you run into during your day is that hobby, though. Have you tried this app ShuffleMyLife? It might give you better things to do outdoors than try to start conversations with shopkeepers.