Run the following on JDK 6u19:

---%<---
import java.util.concurrent.CountDownLatch;
import javax.swing.SwingWorker;
public class Demo {
    public static void main(String[] args) throws Exception {
        int cnt = 20;
        final CountDownLatch latch = new CountDownLatch(cnt);
        for (int i = 0; i < cnt; i++) {
            final int count = i;
            new SwingWorker<Void,Void>() {
                protected Void doInBackground() throws Exception {
                    System.out.printf("Started %d on thread %s\n", count, Thread.currentThread().getName());
                    Thread.sleep(100);
                    System.out.printf("Finishing %d on thread %s\n", count, Thread.currentThread().getName());
                    return null;
                }
                protected @Override void done() {
                    System.out.printf("Done %d on thread %s\n", count, Thread.currentThread().getName());
                    latch.countDown();
                }
            }.execute();
        }
        latch.await();
        System.exit(0);
    }
    private Demo() {}
}
---%<---

You might expect a bunch of interleaved jobs, with #1 - #10 (SwingWorker.MAX_WORKER_THREADS = 10) starting, then some finishing, others starting, and finally #11 - #20 finishing. Instead you see

---%<---
Started 0 on thread SwingWorker-pool-1-thread-1
Finishing 0 on thread SwingWorker-pool-1-thread-1
Started 1 on thread SwingWorker-pool-1-thread-1
Done 0 on thread AWT-EventQueue-0
Finishing 1 on thread SwingWorker-pool-1-thread-1
Started 2 on thread SwingWorker-pool-1-thread-1
Done 1 on thread AWT-EventQueue-0
....
Finishing 18 on thread SwingWorker-pool-1-thread-1
Started 19 on thread SwingWorker-pool-1-thread-1
Done 18 on thread AWT-EventQueue-0
Finishing 19 on thread SwingWorker-pool-1-thread-1
Done 19 on thread AWT-EventQueue-0
---%<---

i.e. only one job is run at a time! The reason seems to be that getWorkersExecutorService seems to ignore this note from ThreadPoolExecutor's Javadoc:

"Using an unbounded queue (for example a LinkedBlockingQueue without a predefined capacity) will cause new tasks to wait in the queue when all corePoolSize threads are busy. Thus, no more than corePoolSize threads will ever be created. (And the value of the maximumPoolSize therefore doesn't have any effect.)"