I think number one is a really bad idea. There are too many free alternatives, and Hubski, for all its wonder, is not unique enough to warrant paying. Honestly, I wouldn't bother to get a one-time use number for that, especially if it was a nominal fee. I imagine I'm not the only user who would end up leaving. And unless those 30 days were especially magical, I doubt Hubski would continue to grow. I see it becoming the online equivalent of a stagnant gated community.
It costs $5 to get an account on MetaFilter. It seems to be working for them. They've been that way for a long time. Heck, people even donate to the site after paying the entry fee. I'll admit I don't have an account there, but I could see it happening. The issue I've had with MetaFilter isn't that they want money to join, or their community. It's that their comments are a flat list. I doubt Hubski would continue to grow. I see it becoming the online equivalent of a stagnant gated community.