On the ranking charts, I'm sure some would find usefull to have the possibility to chalange a player on the spot. Same like paying members have at discussion boards: after the player's name there's an icon to send him/her a message and then another icon to challenge for a game - this is what I'm talking about.

I think it makes much more sense to have the possibility to chalenge someone whose ranking you're looking at and comparing to your own than it does having that feature at discussion boards. So if it's here, why not there? ;)