There´s a huge split in public opinion about them. Some people, like me, are proud of them and happy that Madrid will achieve a more modern image as a city. However there is a large portion of the population that are still very much against them. I´ve seen several graffitis saying "CTBA Towers= Urban terrorism". Also in general many elderly people are against them.
Apart from these towers Madrid is spending a lot of money in modernising itself as a whole (thanks to mayor Gallardon) which I am also in favour of, despite probably 5 years of noisy machinery and blocked roads- not to mention the increased taxes we are all going to have to pay. However I think this is necesary to put Madrid up to the standards of more modern capitals in the world and improve the image of Spain worldwide, which I get the feeling many still think all of Spain looks like Andalucia in 1950.
Theres been so much public rebelion against all this building and roadworks that they are showing a lot of ads to try to remedie this:
http://www.youtube.com/watch?v=hBWEhE_Osl4
This one´s quite intesting, showing Madrid about 80-100yrs ago, saying "What would happen if nothing ever happened?"