I was trying to install omniauth and was getting error for nokogiri libxslt is missing. If you are facing the same issue you may solve it using the following command. I have tested it with ubuntu and it worked for me. Its not tested on Fedora but should work.
on Ubuntu 10
sudo apt-get install libxml2 libxml2-dev libxslt libxslt-dev
on Ubuntu 11
sudo apt-get install libxml2 libxml2-dev libxslt1-dev
sudo yum install libxml2-devel libxslt-devel
If you still face issues do write to me.