KGBMan:

Why would you spend time in a make belief, virtual world, when you can see things and talk to people in real life ???

You can talk to people who you would not normally get a chance to talk to in real life.

KGBMan:

Some internet users who spend all their time in it are in the same category.

Spending excessive amount of time engaging in any single activity will probably cause some mental problems.  Would you put people who watch too much TV, spend time at the gym, read books, play sports, or engage in other activity that is not essential for survival in the same category?

KGBMan:

I enjoy couple forums, computer gaming, but actuly replicating real life in virtual ? why ?

Why would I look at badly rendered characters and imagine I'm talking to real person ? Why would I want to buy anything in a place that can be turned off tomorrow ?

You don't have to imagine that you're talking to the real person, because you are actually talking to the real person.  Avatar is just a virual representation of the real person you're talking to, which might or might not resemble the appearance of the person.  Forums use avatars for similar reasons.

You would want to buy things either because you get some benefit from it or as an investment.  Why do people invest in real estate? In stocks? In gold? Anything can happen tomorrow in real life as well, but that does not stop people from planning their future.

KGBMan:

All people in SL need therapy !!

Hehe.  I am sure they have a therapist in SL that is offering his/her services