Long time since last post, but at least a useful bit of information. On Ubuntu 11.04 64bit if you install the flashplugin-installer, either alone or as part of the metapackage ubuntu-restricted-extras you will get…. surprise, a 32bit flaash plugin! Very annoying, also because it does not work very well.
Just install adobe-flushplugin instead: it will uninstall the old version and you will get a proper 64bit version :)