Yum is a great tool for manage dependencies and easy to use.However actually there is a way to speed up the installation.
Fastestmirror is a tool that will help yum determin what mirror is fastest and to use.
To install on Fedora 17

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sudo yum install yum-fastestmirror

Of course you could customize the fastestmirror configuration easily

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sudo vim /etc/yum/pluginconf.d/fastestmirror.conf

So when you next install a package from the network,I hope you could feel it much faster.