I'll add a tip for those using Drycase. I usually insert the iPhone top first. That way, the camera isn't obscured by the armband, allowing you to take geotagged photos of your catch and share instantly with your online buddies if you so choose.
You can even put the phone into video mode and capture some underwater footage of your catch. Definitely check the Drycase blog where they have a video with someone doing something similar. Or the video where they attempted to blow up some devices while submerged in a fishtank.
Technology is great.