Final Cut Pro X has a nice way to help you figure out which clips (or part of a clip) have already been used in your timeline. It is more a workflow than a trick and goes like this:

  1. Favorite the clip (or clip part) you want to use in your timeline by pressing the F key with the desired section selected. A green line will appear at the top of the thumbnail.
  2. Append the sequence to your timeline.
  3. In the event browser, filter the view by favorites and you will see the list of everything you used so far.

As a rule of thumb, always take the habit of selecting clips you want to use as favorite and discard sections you dont want to use as Rejected (backspace). These filters take a few hours to get used to but provide an incredible productivity gain.

Edit: SafeSolvent also suggested to use the Timeline Index which has a search box and display the clips in their order of appearance if you dont need to look at the clip.

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planetMitch

chief astronomer at planet5D LLC
Mitch "planetMitch" Aunger is the creator and mastermind behind planet5D.com — which covers every aspect of HDSLR cameras (and a whole lot of other cameras as well). A lover of photography since his early days, he graduated to selling stock photos to make a little bit of spare cash. It wasn’t much, but it allowed him to upgrade to better cameras as well as computers, and it wasn’t taking money away from feeding his family.
He loves the stories that the still image can tell. In the summer of 2008, he read a story written by Arnold Kim called “I Quit My Job” — Arn is the owner of macrumors.com. He started macrumors in 2000 as a hobby, and by 2008 he was making more money with the site than he was on his day job, so he quit. The surprise to the story is that he was a doctor making more than six figures! Right then and there, planetMitch dreamed about doing the same thing.
September 2008 rolled around, and Canon announced this new version of the incredible 5D — the Canon EOS 5D Mark II. It was the first Canon DSLR to shoot full HD video and the earth moved! (It really was a huge deal in the photography world.) planetMitch knew if there was ever a chance to ride a wave of something he was really passionate about, this was it — and the blog at planet5D.com was born. It is now one of the most popular HDSLR blogs on the planet, and he is making a full-time living from blogging. He couldn’t be happier!
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