Originally, another sign of the impending apocalypse was going to be stones raining down on Sunnydale High. It was cut out due to budget costs.
The exchange between Buffy and Angel where he starts to tell her that he likes her dress, but she cuts him off saying "Yeah, yeah. It was a big hit with everyone." was added in production and not in the original script.
At 43:25 marks the beginning of many "Hero Walks" for both the Buffyverse and the Angelverse. This one has Buffy in the lead, of course, followed by Xander and Angel.
While Joss Whedon had written other scripts for the show before, this was his first turn as writer/director.