If you are seeing proxy authentication dialogs appearing from nowhere now and then, one of the reasons may be the Sun Java Updater. (If you are wondering what jusched.exe is doing in your process list, this is it.)
I knew there was a registry setting for this, but I couldn’t find it on Sun’s web site. Thanks to James McMahon, here it is:
this is a DWORD that should be set to zero to disable Java Update. The process jusched.exe will still start up when a user logs in, but it exits shortly thereafter.
The reason this has become particularly painful lately is that, unlike earlier releases, the Sun Java runtime and Sun JDK installers no longer preserve this value – so you have to reset it to zero each time either is installed or updated.