1) As a clan leader there is nothing more frustrating than building up your clan, hitting global and encountering numerous hoppers! Most are easy to see when they join your clan by there first request, however it would be nice to you could view a new members clan history before accepting them to see how many clans they had been in, possibly even length of time in that clan too.
2) With regards to a hopper, how about a time ban for someone that joins a clan and leaves within the first hour, maybe a 24hour ban before they can join a new clan.
3) Clan mail - as a clan leader again it is frustrating to have a time limit on the in game mail, especially during a war when you want to get several different messages out to people depending on how the war is progressing, I can get co's to at time but also depends who is about, even if it was you can send 5 out in an hour.
4) Final one is relating to an actual clan war, I am sure a lot of people get frustrated when a member leaves mid war and have not used their attacks, this is pot luck at the end of the day to a degree, but how about an option to purchase any un-used attacks so the clan still has a fighting chance?
Look forward to any feedback/thoughts on the above.