Carles López Cerezuela believes Twitter produces some kind of “collateral damage” in human thinking, and on his blog KRLS he relates [es] some of those effects considering the good and bad parts of each one. Besides the already widely pointed out by several analysts, these are some of the mentioned by Carles:

• Trivializes by creativity. The good part: brings to light a huge amount of genius. The bad part: anything can be seen as a game. Everything is fun for Twitter.
• Hashtag as a concept. The good part: Twitter's wave concept based on hashtag (accumulating opinions about a same topic) allows a divided observation. The bad part: strengthens the herd effect.
• Precipitation of thinking. The good part: removes limits of self censorship. The bad part: in collaborative environments, it's usual to consider every opinion as valid. They are not. Twitter doesn't allow to contrast anything. The thinking speeds up to the emotion. You believe what you want to believe.

More on Carles’ post [es].