For those who prefer using feed readers to streamline their online consumption, you can now follow individual + user streams via RSS feeds using a webapp called, simply, Plus Feed.

The first step is to find the profile ID of the user you want to follow via RSS. To do so, pull up any user’s profile on Google+; the long number at the end of the URL is the profile ID.

For example, the URL for my Google+ profile is https://plus.google.com/109358282983793886559/. 109358282983793886559 is my profile ID.

Plug in that profile ID at the end of http://plusfeed.appspot.com/ —so the RSS feed of my profile would be http://plusfeed.appspot.com/109358282983793886559 .

Add that into Google Reader or another feed reader to stay updated with that user’s public stream.

See the article here:
Create RSS Feeds for Google+ Profiles [RSS]