• Improved reliability. The JVM running the applet is isolated from the web browser at the operating system level. If something should go wrong while running the applet, or if an uncooperative applet refuses to shut down, the new Java Plug-In detects and handles the error condition gracefully; the web browser is unaffected.
• Improved user experience. The new Java Plug-In starts applets in the background, so the web browser always remains responsive. Applets appear on the web page as they become ready to run.

A major criticism of java applets has always been their impact on browser performance. This should do a lot to remedy the problem. Another great addition is that you can now use an animated loading gif by using a new image param such as:

<applet archive="large_archive.jar"
           code="MyApplet"
           width="300" height="300">
    <!-- Use an animated GIF as an indeterminate progress bar
           while the applet is loading -->
    <param name="image" value="animated_gif.gif" />
    <!-- Turn off the box border for better blending with the
           surrounding web page -->
    <param name="boxborder" value="false" />
    <!-- Center the image in the applet's area -->
    <param name="centerimage" value="true" />
</applet>

There’s other great stuff, but these are my personal favorites as they resolve long time gripes. You can find the above plus more in the release notes.

[Hat Tip: Henrik Gemal]