What is the most frequent concurrency issue you"ve encountered in Java?

This is a poll of sorts about common concurrency problems in Java. An example might be the classic deadlock or race condition or perhaps EDT threading bugs in Swing. I'm interested both in a breadth of possible issues but also in what issues are most common. So, please leave one specific answer of a Java concurrency bug per comment and vote up if you see one you've encountered.

Do you keep your project files under version control?

Do you keep project files like Eclipse's .project, .classpath, .settings under version control (e.g. subversion)?

Recommended framework for Java Web Services

With an abundance of frameworks and stacks for Java Web Services (Axis2, Spring WS, CFX, Metro, ...), which one should be selected for new projects? What are the pros and cons for each one? How well have they worked for you?