I'd been using an old 20GB iPod, one with the 4 buttons above the click wheel, in the S2000 for quite some time.
http://km.support.ap...353/HT1353_29.jpg
When I got the iPhone 4S, I decided to rename the 3GS to Car Tunes and put it in the car. It played OK, but wouldn't charge(3GS even put up a warning splash screen about charging not supported with this accessory). Turns out the older iPod/radio interfaces only send 12V down the line, as that's what the firewire based iPods need to charge, while the newer USB based devices want 5V. I contacted Neo Car Audio and they have a replacement cable* for the interface that converts 12V to 5V. It arrived a couple days later and the 3GS is happy.
One of the features I really like is iOS 5 added support for sync via WiFi - so I no longer need to periodically bring the iPod in to update my music collection (I have more music than will fit in the iPod, so it loads my music based on when it was last heard - 5* is always on the iPod, 4* only on if it's not been played in the last year, and so on).
Note: WiFi Sync is not enabled by default. You must dock it to your computer and turn on Sync with WiFi. It's found in iTunes at the bottom of the device's Summary page in the Options section. You'll most likely have to scroll the Summary page down to get to it - I missed it when I first went looking for the setting.
One feature I didn't like is the itty bitty text in the music app. It's very hard to read while driving, especially with the stiff suspension in the S2000. I found a slick app, coincidentally called CarTunes, that I'm now using instead of Apple's music player app. There's a setting to turn off artwork reflections that makes the text even easier to read.
http://evolver.fm/20...lists-to-the-car/
http://itunes.apple..../id415408192?mt=8
* There's also a converter that can be had, for quite a bit less than the cable, but the cramped space around my mount conflicts with adding an extra non-bendable inch at the end of the connector cable.
http://www.amazon.co...ack/dp/B00495JZTY
http://spiceware.org...Vehicles/P1000439