I spent some time looking at the java.net community and here are some of my thoughts:

java.net community:
Site: http://community.java.net/
Bloggers: About 300-350 active participants
Postings: About 5-10 posts per day

Top 3 good things:

• Help wanted ads are listed both for developers looking for an interesting project to work on and for those involved in a java.net project who are looking for someone to fill a particular need. Listings are restricted to volunteer openings for non-commercial projects. Paid job listings are on a separate JobsWiki page
  
• Links to success stories are provided (for example, OpenSymphony is a collection of projects that share common goals: good design, real-world applicability and loose coupling). This makes it possible for developers to look at other products & find ways to achieve similar success with their products
  
• Blog listing by topic, date, technology makes  it easy to navigate. The community area also has RSS feeds, weblogs, mailing lists, Wikis, articles, books & archives thus providing a variety of ways for developers to keep up with recent developments

Top 3 things to improve:

• The help wanted ad listings have a few bugs (for example, the search listing for the JDK community does not list any ads. Also, trying to list all the ads results in a blank page)
  
• The link to success stories has only 3 entries. More stories will go a long way in motivating developers and provide a place to showcase successful products
  
• More project tracking statistics that are visible to everyone (for example, page hits, downloads, community & site ranking). This type of information enables emergent development to occur and measures the success of the community