It still amazes me that many people don't try to build a mailing list. Without a mailing list in a niche, its very hard to keep in contact with people that are looking for information.
It used to be difficult to maintain a database. Now, there are services that you can use for cheap to maintain your mailing list.
How easy is it to make money from a mailing list?
If you're in the fengshui niche, and have a new product that has arrived. Just send out an email with the offer. Your customers will be lining up to buy.
Nerf Guns are the rage in 2010. When new stock comes in, the local department store sends out an email to all their customers to come buy.
If you haven't build a mailing list, get familiar with it here.