A number of feature requests have popped up for OOO changes to lead allocation and uneven distribution of leads, but another helpful request would be that leads are allocated based on availability.
For instance:
User A works 9 - 3
User B works 12 - 6
User A has no leads allocated after 3, User B has no leads allocated before 12.
This would aid leads being handled by the user who is working at the time the enquiry comes in, not potentially sitting in an inbox waiting to be actioned.