Continuity mistake: When Gust is chatting up Julia Roberts' character (moments before he proposes she sleep with him) he lights a cigarette. The cigarette is definitely lit as you see a puff of smoke (the shot is over his shoulder) the shot cuts to his face and the cigarette is no linger lit. The next shot and subsequent shots it's lit.
Continuity mistake: When Wilson shouts 'Jailbait' in his office, he is standing at his desk, reaching for a glass with his right hand and holding a yellow note in his left. The camera angle reverses and instantly he is halfway into his chair and holding the yellow note in his right hand.
Continuity mistake: In the scene in Wilson's apartment, with the attractive girl in only a dress shirt, Wilson is talking to Joanne while the young girl is lying on Charlie with her shirt buttoned. Split second later, her shirt is unbuttoned and Charlie is rubbing her stomach. The time was so fast it would have been impossible for either of them to unbutton the shirt.