Disclaimer I am one the co-founders: I suggest you to have a look at Stream.
Stream allows you to create scalable newsfeeds and activity streams without worrying about infrastructure. The integration is also very simple because there are official clients for the most common programming languages and web frameworks. At Stream we use a mixed approach between Fan-out on writes and pull on read. You can also find lot interesting articles about this linked here that's were we started when we build Stream-Framework the largest open-source solution to build scalable newsfeeds (written in Python with Redis and Cassandra as backends).