I think the leaderboard is a fantastic addition to PS, used in the right way it would promote fun engagements.
I have some further ideas which I feel would make it better.
Notify members that they have lead (Daily/Monthly)
One thing is within many communities I am sure most are unaware of the feature, to promote the fun engagement and to encourage activity it would be nice to see members being told automatically.
I'd like to see team members and members separated, create more friendly competition but IMO, team members within sites are always likely to lead. Just look at IPS, it's mostly staff members or popular developers, this cuts so many people who make great efforts. Within my own community, it's usually always me or one of my team members and I think it would be nice to split it up.
I have some other suggestions, however these are the main areas. I'd love to see other clients make suggestions!