If you're interested in using plugins for web publishing, and you're running FMS/A in 64-bit mode, there's a couple issues you should be aware of.
The SDK for 64 bit plugins was just released a couple weeks ago and most developers have yet to update their plug-ins (though I'm sure are all working on it). Since Custom Web Publishing runs as a 64 bit process, basically, you can't use plug-ins on it yet.
And, once updated plug-ins are released, they now get installed in a brand new location. Plug-ins for CWP now go into a new folder, NOT /publishingengine/wpc/Plugins (that's just for IWP now), but /publishingengine/cwpc/Plugins.
I have some more detail in this blog post: