In this example, someone connecting from chichi.hotwired.com. posted a message to alt.animals.badgers. The message ID can be used to view the message within a Web browser - just type it in as a news URL. (In this case, you'd use news:email@example.com, but since I made up this message ID, it won't work.) Also, notice that the first part of the message ID is what appears to be a username. This could be used to tell who posted the message, but since users can usually enter anything they want, it's not that reliable.
You should also notice in both these examples that the DNS name of the connecting computer (crazy.hotwired.com or chichi.hotwired.com) is the only piece of information that could be used to obtain the user's identity. If you normally connect to the Internet through a dialup account, it's likely that the IP address of your computer (and its associated DNS name) will change depending on which modem you happen to connect to at your ISP. This makes it a lot harder to figure out who's doing what. It's still possible, but you'd have to compare access dialup server logs with the news-server logs.
If you're reading news in an office or school environment, it's more likely that each computer will have an assigned name that doesn't change. If a computer is used by multiple people, your identity is more likely to remain anonymous. Since most computers these days are used by one person, though, it's usually pretty easy to match up a computer name with a user's name.
Systems administrators can also configure news servers to require a username and password from people who wish to read messages. If your news server requires this, your identity and reading habits are painfully clear.
It's important to remember, though, that although systems administrators can monitor users, they rarely do so, because they don't want to bother with the extra work. Remember, there's some anonymity in numbers as well. The more people accessing a news server, the more work it is to keep track of who's doing what. If there are only a few dozen people accessing a server, individuals are a lot easier to monitor.