These groups are extremely useful when doing research. When trying to find women who made their living on the ocean, I posted a request to one email list and received more than 100 responses, leading to more fantastic subjects than would fit in a 13-part documentary series. These global gangs can be also useful to pick up lingo, new trends or doing research before making a purchase. Downloading the list of newsgroups available through your ISP can take a while. You subscribe to the groups you want to read and then can download the messages and start communing.
Most sites hosting newsgroups claim to own the posted material.
There have been cases of people not getting hired after a search of the newsgroups revealed extreme opinions. Like any social interaction, you can pick up viruses if you open attachments to newsgroup postings. Don't do it. Email lists rebroadcast email received by the listserver to everyone who has joined the list. You generally should introduce yourself to the list and you need nothing but your email program to participate.