Firstly, developers can use and manipulate this code to be able to use the Desire HD software on other phones. "Well, I thought this was already accomplished?" you might ask, if you remember the previous article on just this subject: Desire HD rom ported to Desire. The difference is that the "rom porting" can be done much more succesfully using the source code. For example, in previous ports there were problems with the camera, which can be avoided if the port is done using the source code.
Secondly, and more importantly to the users of Desire HD (us), this will allow developers to start cooking custom roms for the Desire HD. For example, if you for some reason dislike the new Sense UI, you could replace it with the stock Android UI (which can be seen on for example stock Nexus One devices). Developers could also improve various things with the original interface, or create new roms altogether or using parts of other roms. In other words, the possibilities for the Desire HD are now limitless! Well almost anyway ;P
Something to note is that HTC has previously taken quite some time to release source codes for their phones (HTC Hero for example). This almost immediate release of the source code is a nice initiative by HTC that will be appreciated, and is hopefully setting an example for other Android phone manufacturers worldwide.
If you are a developers or just plain curious you can check out the source code here:
http://developer.htc.com/
