In private conversations in the Brainstorms community we regularly comment on the emptiness of Second Life you usually experience when walking through that virtual world.
For a workshop today I tried to pinpoint where that feeling of emptiness comes from a bit better.

First the numbers. Linden Lab currently reports that SL is about 700 million square meters big.
With a number of 30-40 thousand concurrent users that translates to about 50 residents per square kilometer (at 35.000 concurrent users).
If you compare that to the population density on earth which is 48 ppl/sq. km. (UN 2004 data, just land mass taken into account) this means that the SL population density is about the same as Mexico, White Russia, or Ireland. It is actually denser populated than the US, all of South America, and South Africa.

On the real earth we know where the population centers are and where the vast empty spaces of sparsely populated areas are, like the US Mid-West or the Brazilian rainforest.
In SL however all areas are built up, there are no rainforests, no Great Plains, no mountain ranges.
And we associate built up areas with population centers.

So when we end-up in a more or less randomly chosen location and see it is structured and built up we expect to meet people. When we don’t, it immediately feels like a ghost town. If you enter a village and see no signs of occupation it gives you the creeps, and rightly so. But in Second Life that is the norm, because the population centers are indistinguishable from the ‘nature preserves’.
When we think we are teleporting into inhabitated areas in Second Life we are actually doing something akin to diving into earth’s atmosphere at a random point above the non-blue areas. We would not expect to hit a major crossroads or city then, but do expect so when teleporting in SL.

At those moments when we know exactly where the populated areas in SL are, we don’t feel like we’re lost. Except those population centres are not only points in space, but also points in time. I think population centres in SL are events (like conferences, meetings, concerts etc).

Empty and populated places in SL: points in space as well as time

Also I think people simply have no idea how big SL really is. We are so used to limited expanses of virtual land in games and simulations. (where you literally walk into the horizon, like in the Truman Show)
Although I believe SL is too empty to be able to provide enough random rewarding meetings and experiences, I also think our perception is skewed because of the fact that our usual clues and indicators for population centres don’t hold true in SL.