I would like knowing if there is a way to increase the performance of the command
yum to install and search packages.
I'm a very happy new user of Fedora 16.
What is the problem you're experiencing? Is it slow to download packages or slow to install?
If the download is taking too long you might want to try the presto (yum-presto) plugin.
See 4.4.3. Plugin Descriptions for a list of available plugins.
If it's the installation itself that's slow you might want to disable any plugin you don't need but I doubt that will make a big difference.
Other than that you will have to look into improving overal system performance.
Take a look at Yum caching. http://docs.fedoraproject.org/en-US/Fedora_Core/5/html-single/Software_Management_Guide/#sn-yum-caching
Caches provide three advantages: