Not everyone seems to know why they want to build an online community. It reminds me of this great video:
Here's my take on it.
Step 1) Build an online community.
Step 2) Ask them what products they want, then make those products. Sell these products to them, and encourage them to sell to their friends.
Step 3) Profit.
Sure there's increased brand loyalty, market research opportunities and cost savings on advertising/PR. But if you need an explanation of what to do with your shiny new online community – this might help. It's easier than collecting underpants.