forums are a great place to start looking for the hot topics and those that gain more attention than others, are ones you may want to consider posting about.
Often when I tell bloggers they should track forums relevant to their topics, they think this means you have to post in them. Nope: use forums as a way to gauge what the collective Borg around your topic is wanting to know about. You barely even have to read the forum responses. Just scan the headlines.