Those of you who say we don't need an external iSight now that they are built in, have you ever compared the two?
There is NO comparison. The built-in iSight has very poor color accuracy, and looks washed out. As others have said, they are also fixed-focus. There is also limited brightness adjustments, when you use third party tools like iGlasses (which is indispensable if you use your iSight in anything but day light).
Good luck if you want to use your built in iSight to show something to someone. With the external iSight, you just turn it around, and shoot away. It makes for a great "walking tour" when you want to show off something new in the house, etc. I can never get the internal iSight positioned at the right angle, and still be able to see my screen.
For very casual use, the internal models are great, but for anyone who uses their iSight very often for iChatting, the external is the only way to go.
The different in picture quality is quite dramatic.
I have checked the iSights built into the MacBooks, MacBook Pro's, and iMacs - all look the same.
I really hope Apple comes out with an improved version - one with better low light sensitivity...