Seamless Software Updates is a term coined by Nokia to refer to the pain-free method of updating the OS of your Nokia Internet Devices like the N900.
With the company now defecting to the Windows camp, the maintenance of Maemo 5 has virtually fallen on the shoulders of the community. To enjoy continous updates of your OS from the Maemo Community, you’d need to install the Community Seamless Software Updates or CSSU.
Basically what this does on setup is that it runs a small script which adds the Maemo Community repos to your software sources and tells the Hildon Application Manager to use the custom community repos for updates.
It comes with bug fixes and features such as support for portrait mode in the menu and also the ability to force applications to use the portait mode. It is important to know however, that this software is still under development and only recommended if you are willing to risk a flash of your device.
I have installed it however and find it working perfectly with no system upsets. Installing the CSSU is easy and takes just a few minutes by following the steps on the wiki page. I highly recommend it to all N900 enthusiats who want to enjoy the use of this awesome device for a long time to com.