Merit system has been in the circulation for almost 5 months and as of now the issue of earning merits for new members and even those who have been here for a long period is still a hot topic.
I think if sMerits will have an expiration date, people will be obliged or will become more active in giving merits to others instead of losing it, this will actually helps many members like me.
Theymos has said that he may consider decaying sMerit in the future.
In an ideal scenario, the flow from the merit sources should be sufficient in the forum. In any case, sMerits were going to get used up at some point or the other.