Do you remember my posts back from April 2006... during my prep-works for our local BigDays 2006 road show I discovered - with some limitations in mind - that sidebar gadgets can be created with Windows Presentation Foundation (WPF) via an IFRAME work-around.
See my two posts
Now I was curios if that still works with RTM of Vista and .NET Framework 3.0 because between February CTP and Beta 2 it did not work... and fortunately while searching a little bit, someone else was brave enough trying this, already. Karsten Januszewski tried this already and blogged about it in great detail in within a fantastic posting. Take a look at what he figured out here. He clearly mentions what the limitations are - but honestly, for some situations I definitely can live with these limitations:))