With regards to watermark and screen protector questions.
My 3GS experienced extreme watermarking. The pics I shared are bare iphone4 with the otterbox protector only on the front. It is seamless. It is the one area where I feel like otterbox may have improved the design, the rest just being manipulating the concepts to fit the form factor. Very pleasing touch and responsiveness. After one days use it seems more resistant to fingerprinting, though that may just be what I perceive after so little use.
I am happy to share and assist with questions I can answer.