I love these shorts for running in the hot weather.  I wear UnderArmour compression shorts under them.  They are very lightweight and breathable.  They also have a pocket to carry my key and passcard for when I run at work.  For reference, my waist is 34-36 and I ordered the size Medium shorts -- they fit perfect.

Update [Sep 2011]: I wore these in a 200mi relay this past weekend. They were incredibly comfortable.

Update [Sep 2012]: I wore these in a 2nd 200mi relay two weekends ago. I finally have one with a hole in it. These have seen a LOT of running!

Update [Dec 2013]: Every pair wore through by the end of summer 2013. So, they lasted about two years. I had some cheap WalMart no-name brand and other Champion shorts lasted longer and with more running. I've reduced my rating from 5 to 3 stars.