How serious should we take health and environmental concerns associated with nanotechnology?

From Wikipedia: Some of the recently developed nanoparticle products may have unintended consequences. Researchers have discovered that silver nanoparticles used in socks only to reduce foot odor are being released in the wash with possible negative consequences. Silver nanoparticles, which are bacteriostatic, may then destroy beneficial bacteria which are important for breaking down organic matter in waste treatment plants or farms. A study at the University of Rochester found that when rats breathed in nanoparticles, the particles settled in the brain and lungs, which led to significant increases in biomarkers for inflammation and stress response.

http://en.wikipedia.org/wiki/Nanotechnology#Health_and_environmental_concerns

After all most people think we should not miss the opportunities associated with nanotechnology. Soon we could have nanorobots entering the human body and directly destroy tumors. We could build fuel-efficient airplanes using carbon nanotubes. Are concerns overrated?

What’s your take on nanotechnology?