I got mine with the iPad the day the 3G version was avaible. It has been in the case almot constantly since. I just took it out to take a look. No scratches. A few smudges that wiped off with some monitor wipes. All lettering still crisp with no sign of being rubbed or worn. After a quick cleaning I'd be hard pressed to tell the difference between it an a new iPad. Even my screen is still scratch free, and I don't use a screen protector.The only caveat is that crud does tend to build up around the edges of the screen where the case ends. Cleaning this area is the only reason (besides checking it just now) that I've removed the iPad from it's case. Apple's case hold the iPad very securely, so there is no rubbing going on as you handle it. That would be my guess why 8 months of use have done almost nothing to the finish. As long as you are careful to put it into the case clean it should be well protected from normal use. I use mine for at least three to four hours a day on average.
No. With the protective flap I've never felt a need. And I don't use it in an environment where I'm likely to get grit on on my hands or the screen.