I use Fedora on my laptop, and at first I had a couple of problems with yum, which seems to always believe you’re connected to the Internet. There a special switch: -C, but it didn’t work all the time with me. I was used to apt-get before, which updates its metadata only if you tell it to (via apt-get update). To configure yum to behave the same way, add:

metadata_expire=99999999

to your /etc/yum.conf.
This way, yum will not try to update its metadata all the time. But beware! You’ll need to do that yourself when you have access to the Internet, using:

# yum makecache

Which is the equivalent of apt-get update.

Edit years later: this tip was useful for early versions of yum, its new behavior is way nicer to offline computers, and is no longer really needed.