Don't waste your milestones and achievements. By highlighting them you create momentum.
Momentum is appealing, infectious even. Many wont join any community until they see it has momentum. Then they jump aboard. Momentum increases membership, participation and improves the overall tone of the community.
So celebrate your 500th member, your 50,000th post, your first mainstream media mention, the successes of your members and any clear progress your community has made.
People want to be a part of successful movements, not stagnant failures. Celebrating small wins leads to big wins. The image of momentum becomes self-fulfilling. And if you create momentum, all your work becomes much easier.