One of my clients only has a T1 internet connection so if I start downloading too many updates at the same time people will complain.
If you need to limit your download speed in Fedora (or anything that uses yum) simply add the following line to /etc/yum.conf

 throttle=100k

if you need to limit download speeds to 100KBps (kilobytes per second).

Ref:
http://dailypackage.fedorabook.com/index.php?/archives/37-Package-Management-Week-Tips-Tricks.html