I use my iPhone 4 which is 30fps. If you have the right software to playback the video installed on your computer... Then you can play back the swing at speeds as slow as 0.2x. I just posted this in another thread, but I'll post it here as well.
With my iPhone 4 and the Protosports holster... I'm able to take quality HD video without the camera moving around. This holster is awesome.
Here is a pro tip to help with playback... For video playback on my notebook... I import the video from my iPhone, and then I use a piece of free software from VideoLAN. The VLC player (free download) is awesome - and allows playback speeds of 0.2x (very slow) and makes it easy for me to pause the frames at the positions from A1 to A8, so that I can take screen shots to get photos of my swing sequence (see below).
Why spend money on a high speed camera? This is the power of the iPhone?! Yes it is. And with the Protosports holster, you can take some very nice video of your swing without worrying about camera movement.