My primary issue with bounties is it feels like guild members can sandbag you by holding bounties hostage. I would think bounties should foster good relationships between guild members, not hamper them.
For example: There are two enchantment bounty slots and one stone bounty slot. While someone has one of these bounties, the slot does not refresh in the bounty list. This means that if my routine is to accept and immediately complete stone bounties, I am completely thrown off if someone else accepts a stone bounty and does not complete it immediately. This slot could potentially be held for 24 hours.
A simple solution would be to allow slots to refresh even if a member is currently holding a bounty of that slot.