Managing multiple cameras on your Mac can be a headache, with generic disk images littered across your desktop representing each device.
That's not to mention the problems you may experience with different applications every time you connect a new camera. If you're suffering this problem then I can't recommend Cameras highly enough. It enables you to assign different applications to work with different cameras, makes it easy to see what is connected, and it's all presented in an elegant and lightweight interface.
Despite the name, Cameras actually works with all camera-enabled devices including the iPhone and many mobile phones with cameras. One nice feature of Cameras is the ability to download photos on connection. I often find that Picasa takes ages to detect my camera and when it does, it spends ages building previews. Camera removes this problem by instantly downloading photos to a specified folder as soon as the device is connected.
I also loved the fact that Cameras supports Growl alerts so that you have definitive confirmation when a device has or has not been connected. This is far preferable to the usual procedure of connecting a camera and then wondering whether it connected or not until the disk images appears.
If you only use one camera, then Camera may not be of much use but if you're dealing with any more than two devices, I highly recommend it.