Chrome, like most other modern day browsers maintains a cache of the video or movie that you have watched online on YouTube, MetaCafe, Dailymotion, Vimeo or any other website and it can be retreived until you have the tab containing the video open. As soon as you close the tab or the browser itself, the video immediately gets deleted.
However, if you wish to re-watch it later on without having to stream the video again, you can easily copy it to some other location on your hard drive. Just make sure you don't close the tab after streaming the video. As of Dec 2012, Chrome maintains video cache in the following location:
C:\Users\<username>\AppData\Local\Google\Chrome\User Data\Default\Pepper Data\Shockwave Flash
Replace <username> by your windows account user name.
Now, just browse to the above mentioned location and copy the flaxxxx.tmp buffered video file to any other folder on your hard disk.
Note: Do not copy copyrighted content. Please comply with the terms of the site you've copied the video from.