Are you certain all of your permissions are correct? If you run Konqueror as root, do they show up? I know that might sound funny, but I remember once when I installed some plugins for Opera, and despite having pointed the browser to the directory where the plugins were, they wouldn't work unless I was root.
Another case where I couldn't get plugins to initialize was the command used to launch the browser. I opened it up in xterm once, using Windowmaker, and placed the icon it spawned on the right bar. After that, i'd launch and although the browser came up, no plugins. The command to launch as linked to the icon was /usr/local/bin/opera. This was of course correct, but I wiped all that out and just put in "opera", then hit the icon again (relaunched) and I had plugins.
These two incidents are ways I had no plugins, then figured out how to get them back. This is of course going back in time a bit, and linux. Your results may vary, hope i'm of help. G'luck.
--Q