Not long ago, when you wanted to buy a service or product, you'd call up local stores, ask friends for recommendations, browse the Yellow Pages, or look in the newspaper for a sale. Perhaps you researched the product in Consumer Reports. But today, the Web offers a completely different way to buy products and services and evaluate providers, and user communities play a key role.

Say you need a set of tires. Instead of going to a tire dealer, you can visit an Internet tire store, which will give many tires to choose from and a list of local installers. At the site, you can read candid reviews from customers who've bought the tires you're considering. You might read that a certain tire works great on compacts but not on large cars, or vice versa.

Name the product or service, and people are going online to research and buy it, using peer reviews to make informed decisions. Consumers trust their online peers as unbiased sources, and it's not just people in their 20s and 30s. This mindset is spreading rapidly to baby boomers and beyond.