1.2 is great (the nascent MSVC support is especially promising), but I'm most excited by the ongoing work in nightly to completely overhaul the compiler middle-end. The high-level overview is that the middle-end is being refactored to operate on its own intermediate representation instead of the raw AST, which should open the door to a whole host of improvements in compiler speed and code generation. It's technical debt whose bill is long overdue. :)