I like people who know what they are talking about. People who can teach you a thing or two if you have the time and can read between the lines.
On the other hand, I don’t like people who can do one thing right in their area of expertise and think that this entitles them to express an opinion about anything and that opinion is the ‘correct’ one. Here is an example: http://www.techcrunch.com/2010/01/04/jason-calacanis-top-tech-products-and-a-political-rant/
A somewhat known guy who runs a somewhat known company is giving you a list of his favorite tech products. Everything is fine until he decides to slip in a rant about the Middle East and oil. Here it is:

For over a year, I haven’t visited a gas station and have been able to give the finger to the bastards in the Middle East who believe that women and gays are about as valuable as dogs, and that the freedoms we enjoy in the United States are the root causes of all evil. If Obama had any leadership ability, as opposed to his consensus-building nonsense, he would have taken the billions we’re going to spend in Afghanistan and simply spent that money on electric car and solar subsidies in America. We have to stop wasting our money building schools and bridges for backwards societies that don’t appreciate them and start spending that money on energy independence. There is no reason we couldn’t put solar panels on every rooftop in America, and electric cars in every driveway, instead of spending money fighting enemies that don’t want the freedom we’re promoting.

This shows that he doesn’t know a thing about how politics works, how democracy or what is really happening in the Middle East. For this he instantly earns the dumb-ass title and a nice shiny bumper sticker that he can place on his cool electric car.