Buffy's footwear changes from boots to shoes in the shot where she jumps
off the bus onto the road.
During Buffy's speech, Andrew's position switches from standing in front of a window to sitting on a sofa near Xander from shot to shot.
As Buffy is running across the rooftops, the weather alternates from being overcast to clear skies between long shots and close-ups.
As Buffy runs through the collapsing school her hand moves up and down the length of the scythe, between shots, with no time for her to move it.
Just before Spike's amulet sends out the blast through the roof, an ubervamp is just about to pin him against the wall. In the next shot he is standing in the middle of the area backing up toward the stairs and then he sends out the blast.
At a little past 25 minutes in, a crew member is seen shuffling around in a back room through the window behind Buffy.