Last month, we added support for Stream Markers to the App.net API. The stream marker feature makes it easy to maintain your reading context across different App.net clients.
As of today, alpha.app.net supports stream markers. Please note: this feature is off in the alpha web client by default. Please go here to turn it on.
How it works
Alpha will show your current stream location using a small red ribbon, pictured here:

When you scroll up or down in your feed, alpha will automatically update the state of your stream marker.
To be transparent, implementing this feature in a web application was somewhat more complex than we expected. Given that, feedback and suggestions on our implementation are welcome.
Thanks,
The App.net team