Google has created an IDE for developing Google Desktop Gadgets. It has drag and drop, simple controls, editing of UI properties and an easy-to-use test environment (you can preview the results instantly). The code editor doesn't have any fancy feature like syntax highlighting or line numbering, but you can write the code in another editor. The IDE can be found in Google Desktop SDK.
This new IDE might help you create gadgets faster for the new Google Desktop Gadget Contest, where you can win up to $5,000 if you submit a cool gadget until July 31st.
Oh, and Google Desktop 4 is not beta anymore and it's available in 27 languages.
Related:
Top 10 Google Gadgets
Add gadgets to Google Pages