1. The process of sending merit seems a bit annoying. You've to go through another web-page and select number of merit to be sent and then send it. IMO, it'd be better if it could be sent just by clicking "+Merit" button right within the thread.
2. It'd be much better if you guys allow only one merit by the merit-sender per post. This will reduce fake-merit-exchange or fake-merit-giving. There're people sending tens of their merits to a single post which clearly seems like something fishy.
Merits are not renewable at a level. If you exhaust your merits on one post, you cannot reward again if you are still on the same level.
Also with exception of Jr member, no single person has enough merit points to effect a rank up. So giving more merits score to one post is harmful.
I think the forum worked on this merit system very well taken into consideration most of these fears.