Developers wanting to create panels that plug into Sony Ericsson’s “Sliding Panel homescreen” can now do so - the SDK has just been released. The requirements for the SDK are pretty humane - you need Visual Studio 2005, the WM6 SDK and the latest version of ActiveSync 4.5.
Unfortunately, Sony Ericsson does not specify which programming language(s) can/must be used to create these panels - I am pretty sure that .NET CF developers will be left out due to the way-too-long startup time of the CLR interpreter (up to three seconds on my rx4240).
Amusingly, the SDK ships with a full XPERIA simulator - should anyone of you feel like taking the box for a spin: this is your opportunity…
Further information can be found at Sony Ericsson’s developer network!