This post from Jakob Nielsen, a leading web usability consultant, highlights a couple reasons why creating an internal community such as Salesforce Ideas can be particularly powerful. 

• A company's employees are an actual community with a crucial shared interest: succeeding in business.
• Employees are pre-vetted: they've been hired and thus presumably have a minimum quality level. In contrast, on the Web, most people are bozos and not worth listening to.
• Although some intranet communities — such as those around internal classified ads — are aimed at lightening up the workplace, most intranet communities are tightly focused on company projects. Discussions stay on topic rather than wandering all over the map.
• Intranet users are accountable for their postings and care about their reputation among colleagues and bosses. As a result, postings aim to be productive instead of destructive or flaming.
• Small groups of people who know each other are less susceptible to social loafing, so more users contribute to intranet community features. In contrast, Internet communities suffer from participation inequality, where most users never contribute and the most active 1% of people dominate the discussions.