Description of problem: When issuing "yum install foo" on a 64-bit installation, both the x86 and 64 bit packages are being installed which may confuse users. I know that there is a way to prevent yum from doing it, but the way to go is probably to only install the 64-bit packages on a 64-bit installation by default.
For Fed-8 there is a yum-basearchonly plugin, which does what you want. For Fedora 9 we've integrated the feature into core yum, and _might_ be changing the default policy to only install the x86_64 packages (currently yum follows the Fedora policy, which is to install both).
Good. Then I just want you to encourage to change the default policy ;)