The only physical damage seen so far has been seven areas where space debris collided with the aircraft. It also blew out a tire upon landing.
My gut feeling on this is that the seven impact areas are of the type easily seen with the naked eye. It’s hard to guess how many impacts are probably on the X-37B, not knowing what the orbit(s) was, but after 244 days in space, there should be dozens of very small impacts on the millimeter scale. Some of these would be hard to see without a microscope, others would be hard to see in the tile material used for thermal protection.
Nick Johnson, the space debris expert at JSC said here that the Hubble Space Telescope gets around 5 impacts per square meter per year, and that was back when the space debris levels were less than half of what they are today. The original solar arrays for Hubble had 3,600 impacts after 3 years in space. The Long Duration Exposure Facility (LDEF), which flew in a lower orbit than Hubble, had 34,000 impacts after 5.7 years in space.
Every one of those black dots on that 3′ x 4′ rectangular silver/Teflon blanket is an impact, and there’s about 300 of them. You might say, Roamy, what’s the big deal? Those are little! You’d be right in that those aren’t going to cause major structural damage, but that one in the upper right was nasty, and they do add up. Remember, this was flying at a time when the Space Shuttle was grounded after the Challenger accident and the orbital debris environment was much less severe than it is now. Think about an astronaut that could get hit, a window that could crack (the International Space Station has triple-pane windows for that reason, and the Cupola has window covers), a telescope mirror, a reconnaissance sensor, a CCD camera. This is a photo of the hole made in the composite high-gain antenna on Hubble.
That’s about three-quarters of an inch in diameter, in a quarter-inch thick honeycomb composite. Not the same as a car-door ding in the parking lot.