First of all, the new iTrip allows you to change transmission frequency by turning a dial on the iTrip itself, and a LED display lets you know just what frequency you've got selected at a glance. No more fumbling for the iTrip playlist while you're trying to drive your car!
What's most interesting, however, is the iTrip's use of LX and DX modes of broadcasting. From the website: "This allows the user to adjust for the absolute best possible audio under real-world conditions. Even in the toughest situations, such as large cities with lots of radio stations crowding the dial, iTrip's DX Mode delivers a noise level that's below that of a cassette tape adapter, allowing the music to punch through cleanly. The results are stunning." I know that a number of users have complained about the quality of the signal. I live in a rural area, so I typically get a good signal, but when I'm in Boston I do end up fumbling around to find a good frequency.
I'd love to try one of these out (hint, hint, Griffin). It looks like a nice update. The iTrip is currently being offered at a special introductory price of $39.99US, and works with iPod Photo, the iPod U2 Special Edition, 4th Generation iPods (with Click Wheel) and 3rd Generation iPods (with touch wheel and buttons).
Update: I just discovered that Playlist Mag recently published a review. Check it out.