This idea dates back to the Russians in the 1970s. The surface of Venus is far too hot, and the atmosphere too dense, for Earth life. However, our air is a lifting gas on Venus with about half the lifting power of helium on Eath. A habitat filled with normal air will float high in the dense Venus atmosphere, The atmospheric pressure there is the same as Earth sea level (1 bar). Temperatures are perfect for Earth life too, just over 0C.
Also, just as weather balloons naturally rise to their operating level high in our atmosphere - and don't need to be engineered to hold in high pressures, so it works in the same way for our habitats on Venus. They float at a level where the pressure is equal inside and out, and can be of light construction. It is arguably the most hospitable region for humanity in our solar system, outside of Earth itself...
http://www.science20.com/robert_inventor/blog/earth_air_filled_habitats_will_float_over_clouds_venus_future_home_humanity-127573

I suspect that such a city would be the very best location from which to study Venus itself.