I noticed this first when I was trying to backup my 3G but thought nothing of it. Now I notice that the 'backup' option for my iPhone 3GS also isn't in the menu on iTunes when I right click on the phone.
I'm actually a little confused with mine as well. I've had it since Friday and it has not once backed up in iTunes. Without a manual backup option, I'm beginning to think it never will.
I noticed this first when I was trying to backup my 3G but thought nothing of it. Now I notice that the 'backup' option for my iPhone 3GS also isn't in the menu on iTunes when I right click on the phone.