1. The Swing text components are synchronized, but that
may cause issues between your worker threads and Swing.
If there are two or more threads attempting to call such
methods, then may be a freeze or deadlock.

2. The Observer/Observable things don't know how to
talk across threads. When the AWT Event Dispatch Thread (EDT)
calls a listener, that listener is running under the EDT
rather than your other SwingWorker thread.

A very safe way to handle such things is for listeners
to post a message (somehow) to your worker threads using
a synchronized event queue. When the worker threads want
to update the visual components, they must use
SwingUtilities.invokeLater(Runnable) to cause the update
to execute under the EDT.

You can use the new JDK 5.0 concurrent package or use the
Mutex package available at http://mindprod.com/products.html
to implement your own event queue for communicating between
your worker threads.