The most easy way to download YouTube Video:

Step 1: Find the video you want to download and wait for it to completely finish loading.

Step 2: Minimize your browser (do NOT close it, some browsers delete the temp directory upon closing), and navigate to the directory /tmp

Step 3: Drag the flash file onto your desktop. Voila!

This definitely works with firefox, and probably most other browsers as well. Enjoy!

Update:

This post is outdated and may not serve the stated purpose.