Haven't read much on this but wanted everyone to know that I am having great success using the "Griffin iTrip Universal Auto" FM transmitter in my car to listen to Slacker. It also gives you the ability to charge your BB (using your USB cable) and use your car radio as a speaker phone with great clarity- very nice!!!
I use the Motorola T505. There's a slight sound quality drop compared to fm radio or mp3's form my phone, but it's great otherwise. No more commercial filled radio.
Love the variety and lack of commercials. A line out on th. Berry would be nice, and slacker SQ is definitely lacking. Still, its my favorite app on my storm.
Posted from my CrackBerry at wapforums.crackberry.com