We maintain multiple repositories, many of which have the same rpms repeated in different locations. In order to save space we use hardlinking extensively. The hardlink command does an ok job of finding things to link, but we are only really interested in rpms and don't want repomod.xml or comps getting linked so I wrote a little python script to hard link all the rpms based on a checksum. The script is over at my github. hardlink_rpms
Our aliases are spammed like any other account, but filtering on them would require making a real account. I wanted to be able to filter aliases without creating accounts for everything. My first solution was to create an account and filter on that one, then using $original_local_part I could forward to a filtered alias. This works but if someone discovers the filtered alias, they can bypass the filtering.
The leap second has had been a problem for Java apps (389-console for me) and apparently some ruby apps (seems like puppet ((can't prove it)) ). I found the common fix is to just set the date based on the current date as shown here.
Doing this on all the machines, a single line with func.