I got an email that ANTS Profile 4 was released, so I downloaded my upgrade and poked around with it this weekend. I haven't given a good look at the new features list, but the performance improvements are very apparent when profiling. There is still some degradation of your app performance when profiling, but nothing at all like it used to be. I no longer feel like I'm suffering through horrible performance for the sake of finding my issue.
The other big-money change is nice calltree/methodgraph with the shiny "Call Graph" that brings you right to the line of code in the Line-Level Timings view. I love interactive + pretty! Native support to export to PDF and PNG too. This is either a new feature or something that's just been made much more discoverable, because I would have killed to have this in 3.x when debugging memory issues.
It's very much worth doling out dollars for.