The trick used here exploits the google chrome cache, all the videos you watch on youtube (excluding those watched when you are incognito) are stored in your desktop in the cache folder here
C:\Users\<username>\AppData\Local\Google\Chrome\User Data\Default\Cache
so watch a video on youtube, finish it, then go to the path mentioned above, and look for a huge file named something like this f_000f18 (sort items by size to find the biggest cache file)
rename that file to f_000f18.flv and you have your video. ta-da
C:\Users\<username>\AppData\Local\Google\Chrome\User Data\Default\Cache
so watch a video on youtube, finish it, then go to the path mentioned above, and look for a huge file named something like this f_000f18 (sort items by size to find the biggest cache file)
rename that file to f_000f18.flv and you have your video. ta-da