* Giving excessive importance to estimates
Seen this one. It was used as a excuse not to do code reviews because they cause to miss estimates. "Look, the feature is done, but because of the code review requirement I cannot mark it 'done' in the project plan." Solution: abolish code reviews.
* Assuming that good process fixes bad people
This one is a big one. It's everywhere. Especially in big software development companies, such as Microsoft and Google. They tend to believe that once they institute a perfect process, everything works out perfectly. Perfect coding guidelines lead to perfect code, no matter who writes it. Perfect testing process - testing can be done by monkeys. Perfect project management process - now we can hire project managers with just basic Microsoft Excel skills. They don't understand that without actual talent the company enters a "spiral of death" which is impossible to escape.
* Ignoring proven practices such as code reviews and unit testing
This is done frequently by people who never tried such techniques as code reviews and unit testing. If you do it consistently through, say, one release cycle, you start to value those techniques and understand their importance.
Unit testing, for example, helps me to avoid painful debugging complex issues in production. All features that I unit tested usually just work when integrated into the rest of the product. In fact, the last bug I had to fix happened in code that I neglected to unit test, because the unit test setup was too complex for that component (in itself an indirect sign of a problem). Unit tests also lead to components usable independently of each other, thus reducing the overall system coupling.
* Hiring developers with no “people” skills
This is a double edged sword. On one hand a developer who can't communicate well will eventually produce code that doesn't do what's intended. On the other hand there are people with too much "people" skills who can't code shit. They just bullshit their way through. I'd say there are too many of such bullshitters. A lack of communication skills in a developer is a problem fairly isolated to that developer. A lack of coding skills in a bullshitter is much bigger problem that affect many people around him.