We have just tested the TightVNC 2.6 Java viewer on Mac OS X. This generally works well in 10.7 and 10.8, but there's an interesting problem in 10.6: Keystrokes don't seem to be accepted until the user clicks one of the buttons in the toolbar.
Steps to reproduce:
* Log into a Mac OS 10.6 machine, and make sure the latest Apple Java update is installed. Currently this is 1.6.0_43-b01-447-10M4203.
* Fire up your browser of choice. We've reproduced this behavior in Firefox, Chrome and Safari.
* Connect the TightVNC 2.6 Java viewer to your choice of VNC server. We tested with TightVNC 2 on Windows and X11VNC on the Mac.
* The viewer displays the remote screen, but keystrokes are not accepted, and don't seem to have any effect at all.
* Click on any button in the TightVNC 2.6 Java viewer toolbar.
* After this point, all keystrokes are correctly handled.
* Keystrokes are always correctly handled on 10.7 and 10.8, so I believe this problem is specific to 10.6 - or more likely, the specific version of Java shipping on 10.6.
* We have not seen the problem in any version of Java on Windows.
* The old TightVNC Java viewer did not have this problem on 10.6 as far as I'm aware.
* From a quick Google search, this doesn't appear to be a known problem - so it could be environmental. But we've tested on several 10.6 machines, and all of them have behaved the same way.
Happy to provide additional information if required.