So in the course of working on posterous, I've had to fix a fair share of bugs where JS works in Firefox but not in Safari. At first I grumbled... but actually, now that I have it installed on my Windows machine... I am dang impressed.
It is FAST. The fonts look beautiful. Things don't pause unnecessarily. It doesn't crash as much. Handles lots of tabs well. I love the treatments on buttons and clickable items.
If it had plugin support for my bookmark syncing, I'd consider using it 100% all the time. Who would have thunk it? But Safari is giving everyone else a serious run for their money. It's got the superior user experience right now. Tell everyone!