5 google wave invites

If it takes a day and a half for a chicken and a half to lay an egg and a half, how many days does it take a monkey to kick the seeds out of a watermelon?

If you put your two cents in and someone gives you a penny for your thoughts where does the other penny go?

I move effortlessly between places and groups of people,
Shifting, traveling, collecting where needed,
Visible but hardly noticed,
Hardly noticed but ever present.
In fair circumstances, I am light, versatile, a dancer in the wind;
Under pressure, I am hardened, powerful, tougher than you could
ever imagine.

What am I?