My proposal - a value add donation system. It can be built up later, but it starts with purely mechanical practicality.
The first thing that people get for donating is servers that stay online. It's not sexy and it's not supposed to be, the sexy ideas are for when we need to attract people, but right now there's a constituency of users who want to contribute to the site.
This dynamic, willful donors and a service in need, has been thoroughly explored by nonprofits like NPR and PBS and they go with a straight donation model. It could easily be replicated on hubski by, once a quarter, having a jimmy wales style bar that shows how much in donations is needed to pay for the servers for the next 3 months.
What's interesting though about the NPR model, and this was more true in the 90's, was the swag. Swag added a bit of social currency to the donations by giving away "limited time" coffee mugs, bumper stickers, sweaters, and other visible badges of support.
Hubski could create similar social value through a digital badge system. In my mind there are two valuable types of donors - those who donate regularly and those who donate a lot. To account for this each profile would get two badges: one that progresses for every time you donate, one that progresses in relation to how much you donated.
In theory, this creates a system where people's financial donations translate into unobtrusive social currency. The problem is that a very similar system was created with reddit gold and that wasn't enough to support them, but I'm hoping the smaller size and different makeup of hubski can counteract that.
Another problem lies in people who don't want their donations to be public. This could be addressed by allowing people to turn off their badges.
The benefit is that it creates the foundation for a system that converts money to social capital which could hopefully expand with the needs of the site.
Swag is the key for me. I will pay extra for something which supports a cause I like, where I wouldn't give the actual cash at face value. Would I give NPR $20 even though I should? No. Would I if they sold me a $20 t-shirt that cost them $5 to hand out? Yes I would. I want a hubski t-shirt. Sell that for $20, keep the profit to run the site, done-zo like Funzo.
http://www.redbubble.com/people/hubski/shop The are hubski goods, which I'm assuming go to support the site, they just aren't very visible.
That's a major problem in selling something. As well, I'm not aware of how much of my money goes back to Hubski on that site. That's a major difference in buying a t-shirt that supports Hubski and supporting Hubski and getting a t-shirt in return.