Copied from my post on ls1gto.com,
I wanted to record video while racing without my wife in the car. I really wanted a GoPro but decided it was too much and I love the video quality on the new iPhones. So after researching different windshield mounts I landed on the Arkon IPM515. It is auto adjusting in size so I can use it with my case still on and it has a very sturdy mount similar to a nice GPS. I made sure to record video with my horrible quality 3G S and my wife's iPhone 4 (for some reason it didn't upload in HD ). I am probably going to get a 4 S or iPhone 5 when it comes out so I can have 1080p video!
Here are the 2 videos I recorded in the WRX (I'm sidelining the GTO to fix the driveshaft, sorry!) I noticed that with my skull candy case on my 3G S there is no vibration like the iPhone 4 with the "bumper" case. I think this is due to the part that grips the phone is right up against the speaker on the 4 and the skull candy case keeps the grip further away.
$10 Camera mount for iphone in 06 WRX (3G S) - YouTube
Towards the end of this video I try changing the camera angles a little bit. Enjoy.
$10 Camera mount for iphone in 06 WRX (iphone 4) - YouTube