On the Internet it's normal to use ты to an unfamiliar person, but in the real life you should use вы towards strangers unless the person you're addressing to is a much younger than you are (a kid or a teenager).

I would feel like a dork talking to somebody in the 2nd person plural if they were around my age when it wasn't culturally necessary.
When you're relatively young (say 20+) and you're not on a formal occasion, it would be probably safe to use ты towards a person of the same age. If you are on a business negotiation, you should use вы.
You can agree with somebody you've just met to use informal ты with each other (and you're automatically on a friendly terms if you drink vodka together )

It goes almost like this -- if you would use Mr or Mrs you should use вы, if you can say 'Hey, you' then it's safe to use ты.