Have just posted on Kenai a summary of common problems found in Ultrastudio.org java applets. There are some general tendentions that may give valuable hints on that went wrong in the past. While I myself simply placed "download the latest version" on my site, many applet developers really tried to keep they applets runnable under 1.1 or 1.0, even adding numerous classes of that looks like a rudimental implementations of they own Swing. Other shared problems, also covered in the review, are event handling, GUI designers, resource loading and animation threads.
The summary can be found in Kenai forum