If it ain't broke ...

I am a regular apologist here for market-based solutions. It seems clear to me that the market is the best mechanism known for getting people to work together toward ends they value. It is often described in terms of competition and greed, but the former is really a competition for opportunities to cooperate with others in voluntary exchanges, and the latter is an ugly label for the healthy self-interest that directs us all to do what's best for us and those we care about.

The market-based model encourages a healthy, spontaneous order among millions of strangers who might not otherwise have incentive to work together. "It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest." But the market is not best in every case.

Our household is run on collectivist principles. We have one bank account. Most property is held in common. The junior member has relatively few freedoms compared to the adults, who exercise authority that is not always egalitarian. Similarly, my workplace exhibits hierarchy and favors.

When a relatively small number of people know each other and are interested in each other's welfare, the market model may not be ideal. Perhaps communities up to around the size of Dunbar's number, like Amish towns, function better on collectivist principles including kindness, group responsibility and authority.

Hubski seems, for now, more like an Amish town than a global marketplace. There is some question about how well it will scale, but in my experience it has already scaled far beyond the point at which I feel I know most users, yet it still feels generally friendly.

it will keep out spammers

This assertion is made without evidence. Does offering financial reward for posting really discourage spam? It is possible that monetizing will have the unintended consequence of encouraging spam. Right now, one of the reasons people refrain from outright promotion is that it would appear crass and inappropriate in a discussion forum, where we users are like guests at a party. When you require people to pay to post, they may feel entitled to post whatever they like: it's their right, they paid for it.

The day care center is a suggestive example.

it will probably limit useless comments (for example, the other day I got a million upvotes for whiting a smiley face)

That evidence suggests that such useless comments would be encouraged rather than discouraged.

Third ... social capital ... a cool internet experiment.

It would be interesting to experiment. I know I would not be able to resist the temptation to accumulate social capital and move up on the scoreboard. I might give up my habit of attaching lengthy comments to stale posts and instead rush out quick crowd-pleasers for hot topics.

If the Hubski masters wish to offset what must be considerable server costs, I think a donate button is the simplest answer.