That is a loaded question because it all depends on several things which are not static. 

1. How much you need to live on. 

2. What you charge for your site membership.

3. The nature of the site itself (ie. mainstream or taboo)

4. How you run your business.

5. Rate of member attrition. 

6. Your market capture.

In a perfect world i would guess about 132 "paying" members each month.  If you charged $19 a month per member would equate to about what the average (not minority) person brings in a month working outside the home which is about $2500 a month.  

Dave

I think that is no easy have 132 paying members if the site is only 0-1 years old.

the next question to follow this question is:

How long time would it ""normaly"" take to have 132 paying members very month?

1 year?

2 years?

3 years?

5 years?

I know the time so different but if we give a medium time stamp some where in the middle value.

Marcus

It really depends on many of the same items as before.  Just having a niche site is not good enough anymore, it takes financial backing, and get up and go. Turning over every rock you find and 1 out of 50 rocks you might find a member.  And then you have to convert the member into a paying member which is another long shot many times.  

I would say several years at best even in a perfect world. 

Having a social site can be fun, exciting, and even fruitful over time.  It can give you skills sets that you would not otherwise ever get.  However it can also be time consuming and take over your whole world as well and many fail because they either do not do it correctly, they have no marketing plan, no get up and go, no sales plan, or no financial backing.  

One reason why it is so difficult is because you are against the odds to begin with. First you have to realize that very few people are going to register for a site that only has 5 people, even 100 people they are very hessitant.  Usually at 500 members you tend to see the curve turning in your favor slowly.  Because the site is active enough to keep people interested so they come back. 

Some sites fail because the admins refuse to do the member build up properly, one member at a time and keep them active.  They resort to fast solutions like purchasing member profiles from sleazy (yes i said sleazy because many of them are just that) profile merchants who sell human data profiles.  

You ever wonder how some sites "one day you never heard of them" and then the next day they have 100,000 members, well odds are they purchased the profiles. Which in my opinion is underhanded and malicious in its own way. 

Also you have to get your local market first, not everyone understands that.  Your local market will sustain you as you grow a wider circle of members. 

So bottom line is i don't know how long, but i can say i closed one of my sites down after 4 years and only 150 members. Many things factor into your question.  Ask yourself why does one person succeed when another fails when they seem to do the same tasks.  Who knows why, i guess the answer is somewhere in the universal makeup.  

Dave