After experimenting briefly with a beta version, I have determined the best new feature of Windows Vista.
I complained back in 2001 about the rough edges on large form buttons in Internet Explorer. After installing Internet Explorer 7 on Windows XP, this was one of the first things I tested. I was dismayed to discover that the problem still persists.
However, on Windows Vista using IE 7, the corners of wide form buttons are not broken. That alone is worth years and millions of dollars worth of development.
That said, I still don’t understand what determines how wide the form buttons actually become (seems to be some kind of length_of_button_text × 1.N formula).