It's on the master list of 3.0 features, but we've been sent enough tips and suggestions about it to conclude that the advanced podcast/audiobook controls came as a pleasant surprise for lots of iPhone and iPod touch owners who upgraded.
In the 3.0 version, from the playback display for a podcast, tapping the screen brings up a set of expert controls: a button to email a link to the podcast's page on iTunes; a 30-second "What's that, now?" instant rewind button; and a playback speed control to give you 1/2 speed, normal or 2x "FedEx mode" playback.
The scrubber bar itself has been given a charge, even though it doesn't look any different until you tap it; it displays the relative playback position within the episode being played. Dragging horizontally gives you high-speed scrubbing (previously known as "just plain old scrubbing"), but if you keep your finger on the screen and drag down, your scrub rate lowers step by step through half-speed, quarter-speed and 'fine scrubbing.' This detail control makes it a lot easier to cue up a particular spot in a long show or book chapter.
I've started to enjoy listening to some of my longer subscriptions in 2x mode, especially when I have a fixed amount of time to listen to the podcast but I still want to cover as much of it as I can. Even shorter news-centric podcasts can sometimes benefit from a speed boost. If any of you try out the 2x mode on an audiobook, do let us know how it works for you.
Surprisingly, I find myself using the 'email this' button quite a lot, especially to let friends and family know about some of my favorite shows. I imagine they'll be getting tired of that pretty soon.