As this has never worked right out of the box (the necessary files are in places not expected by the gem installer), here is what I do:
sudo gem install mysql -- --with-mysql-config=/usr/lib/mysql/mysql_config
you are a Fedora (9) user and try to put a remote HP scanner (in my case, it is inside a LaserJet 3055 All-in-One) to work, do not forget to install the separate scanner driver package libsane-hpaio. All the goodnes of the HP Linux tools and xsane ends in frustration (about the scanning part) if you fail to do so. Otherwise, I would like to state that I am pretty satisified with that particular device and its indifference regarding operating systems.
There is one feature of yum in Fedora 9 I was not aware of: if, during an installation, you feel unsatisfied with the download rate provided by the current mirror, you can just hit Ctrl-C once, and yum will cancel the current download and try the same file from a different mirror.
(6/7): blabla.fc9.x86_64.rpm (30%) 23% [========== ] 11 kB/s | 384 kB 01:47 ETA Current download cancelled, interrupt (ctrl-c) again within two seconds to exit. (6/7): blabla.fc9.x86_64.rpm | 1.6 MB 00:02
Apparently, that fancy piece of javascript in the side column is somewhat broken. Last time I looked, it promised the release date for Fedora 9 to be in 13 days. Today, it says 25. Hopefully. it gives them time to bake in some more fixes.