Re: F18 Yum Update query
That is entirely up to you.
I have had excellent results with leaving the updates-testing repo enabled on my machines here, but there is a chance that an update will get in there that might break something. It hasn't happened often, but it can happen.
If you disable the updates-testing repo, it will be a little longer before you receive the update, but it goes through a little more user testing before being pushed to the regular updates repo.
It's mainly just a matter of choice whether you enable or disable the updates-testing repo.
I would recommend that if you have kmod packages installed from rpmfusion, and you have the Fedora updates-testing repo enabled, then you also enable the rpmfuison updates-testing repos so that you will get the kernel modules when you update your kernel.