Chris Spooner has written up a very thorough tutorial on how to create a self hosted Lifestream. This tutorial takes you through creating a design for the site as well as the individual feed elements, coding the site using XHTML/CSS, and then using SimplePie to power the importing of all your feeds.
He provides images outlining each step of the process as well as detailed code samples in the post. He even provides a downloadable package of all the code used in the tutorial. I looked at the code he provides, and it’s very clean and simple. Only a single 73 line php file, stylesheet, and the SimplePie code, although I highly recommend downloading the SimplePie code from their site and also viewing the tutorial on it Chris has provided.
This is a very nice writeup that provides good information for anyone trying to roll their own Lifestream. You can also view the site he created from the code here.