When Linden Labs introduced the Windlight atmospheric rendering system in the latest First Look client, I was surprised at how much it really enhanced the experience. Clouds now render on the fly, and have movement and reflection, just like a real sky. The sun reflects off of the clouds and the resulting colors reflect to the ground. It is hard to explain, but it makes everything feel more realistic.
One of the things lost with this upgrade was the ability to fly in to the clouds… entire builds were done in the old clouds for effect. To answer that, Linden Labs is planning to introduce Nimble. Nimble is a remarkable cloud enhancement that actually allows you to fly through the artificially rendered atmosphere.
Those of you that don't get Second Life right now will look right past these developments as uninteresting. But remember this post in 5 to 7 years when you fire up your 3D internet browser for the firs time (likely a derivative of today's Second Life) and see the atmosphere for the first time.