Corrected entry: In the scene at the apartment where Vika, Anne, and Natalie are scavenging supplies, an alien sees them from outside of the building through a window. According to the shopping center/mall scene the aliens cannot see a person through glass, therefore the alien shouldn't have been able to spot them through the window.
Corrected entry: In the scene where the 5 survivors come across the downed Airliner inside the hotel, there is not a single burn mark from a fire or explosion and seems as though the plane was just laid there for effect. Any airliner even one nearly out of gas that crashed out of the sky into a building would have burst into flames and exploded.
Correction: The main reason planes explode or burn when they crash is that you get electrical sparks (planes are filled with wires) combined with highly flammable fuel. In the movie the aliens "steal" all electricity, which is the reason the plane crashes. With no electricity in the plane it would just smash into the ground (sparks from metal against concrete _could_ ignite the fuel, but that depends on how the plane crashed into the building, so it's possible).
Correction: The window is open so the alien would be able to see them.