As with most technologies, Eclipse started out with a single newsgroup. Now, all major, and some smaller, Eclipse projects have their own newsgroups. Some are more active than others. Some have a very specific scope, and others are more broad in their coverage of discussion topics. The Eclipse newsgroup page has a complete index of the current Eclipse newsgroups and a description of their focus areas.
The most active newsgroup has around 1,500 postings per month. Before you post a question to any newsgroup, it makes a lot of sense to search the platform newsgroup for an answer. Chances are that the question has been asked before, and the answer can be found there quickly.
The newsgroups are archived at the Eclipse Web site, and the search engine at the Eclipse Web site can search them quite efficiently.