Only a few at most. The more people that get involved, the less time and attention you can keep up with each of them. For example, on social networking websites, for those that have tons of people on their friend list, I'm certain that they don't all keep up with each other at much, if at all. With just a few friends, it's a lot easier to manage and have those that are closer to you than more friends where there's a greater chance of misunderstandings and problems.
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The world is a very nice place, depending how well you fit in...
The Internet; human stupidity at its finest...