When taking video with any mobile phone the problem is hand shake as one can never hold the handset steady enough, this even applies to the new iPhone 3GS.

However, this problem may well be sorted for the iPhone 3GS as wired reports on an iPhone 3GS Shoulder Mount Accessory, which enables you to hold the iPhone 3GS steady enough to take perfect video.

It does look somewhat cumbersome and maybe takes thing just a little too far, but it does seem to improve on video quality. There is a video of the iPhone 3GS Shoulder Mount accessory which can be viewed for going here.