Corrected entry: Spike decides he doesn't want to see the world end and makes an alliance with Buffy. Later on, however, he helps Angel get the information he need from Giles to end the world. If he's trying to save the world, why help Angel destroy it even faster? He didn't need to buy Giles any time - he had already convinced Angelus to keep Giles alive for the time being. If he had truly reached breaking point later on Spike could have called in Drusilla then, but as it is he helped Angelus way too early and nearly cost Buffy her life. (00:09:00 - 00:23:00)
Revealing mistake: When Buffy breaks into the locker, the locker is already damaged. Probably from a previous take.
Suggested correction: Watching the scene, the only real damage is a slight dent that isn't all that close to the lock (she basically punches out the lock to open it). And to be perfectly honest, a dented locker isn't out of the ordinary for a high school. I saw plenty of dented, bent and damaged locker doors all the time back in high school. It's entirely probable that it is damaged from a previous take, but I think it's also within that sort-of realm of possibility (since like I said, dented lockers aren't out of the ordinary) that it might not be considered a mistake. I'll leave it up to people's votes.
Correction: Spike wasn't helping Angel, he was biding his time, playing along and trying to keep Giles alive, until Buffy could get there.