I run CentOS 5.2 x86_64 on my workstation at home. Since 5.2 came out with nepluginwrapper bundled into it, none of my plugins work. I thought it was just a problem with the flash plugin, but neither the mplayerplug-in plugins nor the adobe acrobat reader plugin work, either.
I have no problems with 32-bit flash and 64-bit mplayer plugins in 64-bit Firefox. Haven't tried adobe acrobat yet.
For flash plugin to work with 64-bit browser you need to install both x86_64 and i386 versions of nspluginwrapper with all the dependencies and run mozilla-plugin-config -i