With design complete, pages, scripts and links programmed and the tests done, it's time to roll out the site. Ta Da!
You should have developed a promotional plan. Now's the time to implement it. Make this a priority and make sure there's someone responsible for carrying out the plan.
Be fanatical about monitoring your traffic. For the first couple of months your site is up, you'll want to review your usage logs every week. Look for surprises, both good and bad. Be especially alert for new opportunities.
Follow up aggressively to make sure that the back office is working the way it should. Are orders getting handled properly? Is email being answered promptly?
Watch out for unintended consequences of all kinds. Be hawklike when watching what happens to folks' workload. If someone starts to get overloaded, shift some work around before performance and morale suffer.