There are thousands of discussion groups and community forums covering hundreds of subjects. You can listen, engage, or be engaged as you wish. No one can see you sweat, and you don't have to feel like a wallflower since no one can see you standing off by yourself. Many recruiters are lurking the lists to find potential candidates. In fact, it may be harder because you can't really establish a true personal relationship online.
First impressions count even more.
Be very careful with your first public posting. Your online behavior matters more than you think. You may chuckle at that last one, but a friend of mine who participated in a mailing list for professional engineers told me that one participant on the list was so nasty online that no one would attend his presentations at conferences nor refer business opportunities to him. Talk about having your online persona affect your offline professional reputation. Listen patiently to the mailing lists or newsgroups you have joined and learn the tone, language, and culture of the group.