1. Pretty much all the series were filmed in front of a live audience at Burbank, California. An episode generally took at least 5 hours, with twenty minutes between scenes to swap the sets. Around 300 fans turned up to watch each, with only cliffhangers not being included in the live filming.
2. Before the show aired, the Director James Burrows (for some shows between 95-97) took six members of Friends to Vegas. Whilst at Ceasar's Palace he apparently said that once the show went live, they would not be able to go somewhere again without being hounded by fans.
3. During Season 2, the six cast members refused to work until they all earned an equal salary of 100,000 dollars per episode. Apparently they earned 22,000 during the debut series and by the final season, each member earned around 1,000,000.
4. Fans of Friends were left confused when the show decided to swap the apartment numbers. Monica used to live at 5, but swapped to 20 as producers realised it made more sense (due to Monica living on a upper floor).
5. Actor Bruce Willis made a surprise appearance on the show for free (providing his money to charity) after losing a bet to Matthew Perry. Willis apparently gambled that film, The Whole Nine Yards, would not be a number one in the box office on the opening weekend. In February 2000, he was proved wrong.
6. Some Central Perk cafes have opened, inspired by the series' famous coffeehouse. Downtown Beijing was the first host, with a replica of Joey's apartment opening next door due to the cafe becoming so popular. Another opened at Liverpool in 2012 (before shutting in 2015).