RSS feeds are not officially supported by Google Plus yet, that’s bad if you want to follow a specific user on the new social networking site. Sure, you could add the user to a circle to read all messages on the Google Plus website, or visit the stream of that user directly to access the new messages.
Both options are not really that comfortable, especially if you do not hang out 24/7 on Google Plus. The alternative? You could try a service that turns a stream into an RSS feed