I saw one of these things "hovering" above the Philadelphia area last summer (I think) and for a couple of weeks thought it was a UFO (in the strict sense, not specifically from Glaxxon-7);. Somebody here on RR pointed me in the direction of Project Loon and sure enough there was one in the area on that day. It was weird because it stayed almost perfectly stationary for over an hour (from my perspective, at least), but at the time it was at like 50,000 feet or something like that. I guess that is normal for high altitude balloons (they sometimes hit the doldrums and appear static).
Good observation. They use the wind speeds at various altitude for steering. Yesterday I was showing 3 knots at times and it was visible for a good 2 hours seemingly stationary. Since they have an N number not a good idea to green laser them (Federal offense actually) but it would probably look very cool from the ground.