Continuity mistake: The tyres on the crotch rocket motorcycles they were riding kept changing from knobbly tyres to road slicks, back and forth depending on what terrain they were on. Easiest to see when Ethan skids on the road to avoid the white van - clear shot of slick tyres - then about 30 seconds later they're on the dirt, he skids into the old car and you can easily see that he's got off-road tyres front and back.
Continuity mistake: In the car chase scene with Nyah after they split and hit again and are spinning look at Ethan's car. The driver's side in the close ups was on the American side, then in the spin it is reversed to an English side. (It is a negative image - the license plate is reversed). The next image is back to normal.
Continuity mistake: In the scene where Hunt is chasing Nyah in the car, there is a part where he almost hits a gray car. When the camera shot comes from behind, we see a gravel road on the side with pine trees, but when it cuts immediately to an air shot, we see a concrete bridge-like road with no gravel for several feet ahead or behind. It does this throughout the scene.
Continuity mistake: Why did Hunt's team decide to use an outback location as their Sydney base? It looks like it's in the middle of the Nullabor, which ain't exactly a helicopter ride from Sydney. Come to think of it, there isn't much terrain like that anywhere within a several hundred kilometres of Sydney.
Continuity mistake: In the rock climbing scene, just after Hunt does his flying jump, he falls, slides down a smooth rock face and grabs a hold at the last minute to stop him plummeting to his death. When he pulls back up, and over he grabs a hand hold on the smooth surface which wasn't there before. If you know what you are looking for, you will also see that it is a bolt on hold which has been attached to the rock face.
Continuity mistake: In the scene where Nyah is walking up towards Ambrose's house, the wind is playing havoc with Nyah's hair and scarf. Throughout the scene, there are several shots of her where there is no wind, her hair is not moving and the scarf is perfectly placed (most noticeably when she steps off the boat onto the walkway).
Continuity mistake: The 747 that crashes in the beginning of the movie has a fictitious airline name painted on the fuselage; but the dialogue uses a different name.
Continuity mistake: When Ethan makes the spectacular leap during the rock climbing scene, you see him land vertically, as in he landed in a standing position, clinging to a rock safely, yet when it immediately cuts to another angle, he is already sliding down to the edge.
Continuity mistake: When Nyah and Ethan are in the tub at the mansion, one shot shows Nyah with the heels of her feet up, then it switches to where they're facing the bottom of the tub.
Continuity mistake: In the first scene Ethan is climbing - he makes a strange jump and he manages to move from one rock to another, but after that tremendous front-hit his t-shirt is perfectly clean...what soap does he use?