When do user-created communities start feeling alive?

How long do we think it’ll take for user-created communities to really gain traction? I know I should ‘be the change,’ but I’m definitely more of a lurker.

I recently read about the 90-9-1 rule (typically 90% lurk, 9% interact, 1% create). So if communities don't hit a certain critical mass, they seem empty. I'm assuming new communities need a strong push from 10 to 20 unique voices to grow over time?

And with that, should Digg consider pruning dead communities at a certain point once the initial mad dash to claim community names is over? I say this as someone who has no intention of starting my own community.

We’re still in the early days of the beta, but what’s the tipping point? Do we need better discovery tools, or just six months for the dust to settle? It’s a cool platform, but I’m curious what others think about this. I'm starting to see a few communities like /guitar and /shitposts hit that critical mass, so I assume it's just a matter of time.