Virtually all major online retail sites, and many minor ones, give shoppers the ability to add their own reviews of products. The trend that once gave brand managers and marketing executives stomachaches is now pervasive, and becoming more important with each passing day: According to a recent Nielsen study, 70 percent of shoppers said they trust consumer opinions posted on retail web sites.

"Online retailers have recognized that letting customers write reviews is very important — it's table stakes," said Matt Moog, president and CEO of Viewpoints Network, which operates the consumer-facing review aggregator Viewpoints.com. "They've also realized that being found through search is critical to a successful retail model, and most retailers don't have a lot of good search-friendly content, so they're all on the hunt for it."

"What helped was that we had already spent quite a bit of time and effort in thinking, in a blank-slate sort of way, how to build an online community that's focused on getting people to talk about products and services," Moog said. "That's different from Facebook where it's more about social life and relationships. We spent over a year doing that, and when we first met the folks at Sears, who were looking to start a community, it turned out we had very like minds."

The collaboration has scaled extremely well — the sites went live in March and have since registered more than 400,000 users and 2 million monthly visits.

Harles said that in the early days of the sites, motivation for shoppers to contribute reviews was simply the ability to be heard. Shortly thereafter, they implemented a reputation system that gives "badges" to users based on their level of involvement — users that write a lot of reviews or get a lot of friends will receive corresponding kudos to display on their profile pages.

"And we're gradually experimenting with small incentives — usually not monetary ones but soft benefits like sneak peeks and advance notice of things that are hard to get," he added.

Also key to the sites' success, Harles noted, is the ease with which users can go from casual user to active contributor. "We are one of the first major retailers to sign up for Open ID," he said. "We're going to intercept people where they are. You can use your Facebook or Twitter or Yahoo or Google account to log in, if you want."

Turning online shoppers into a community

Retail consultant Mike Wittenstein offers these four practical tips for retailers wanting to turn their browsers and buyers into generators of content:

1. Just ask. Go through product registration cards and invite people, especially those with multiple purchases in a single category and those who have shopped online in the last six months. Among that group, home in on store credit cardholders first, inviting them to join an "advisor's circle" to kick-start the community pages.

2. Offer an incentive. When review aggregator Kudzu launched, for instance, they paid for the first few entries under each company. Manufacturers and brands could potentially foot part of the bill for this.

3. Use data mining to determine which products already have online reviews (on the manufacturer, brand and/or distributor web sites). With proper permission and attribution, port those reviews over to get the flow of content started.

4. Enhance contributor profile pages, without revealing personal information, so that browsers are attracted to reviewers with similar interests — for instance, a review of a dishwasher might resonate with parents if the reviewer is designated as "Mother of three, two of whom are infants with lots of bottles to rinse."