Posted by Andrew.
I created a bookmarket to download YouTube Videos in Google Chrome on Oct 05, 2008. However, many readers leave comments to tell me that the bookmarklet can't work fine since last month.
I just checked the YouTube site and noticed that YouTube modified the video parameters. If the old bookmarklet can't work on your Chrome, please use this:
javascript:window.location.href = 'http://youtube.com/get_video?video_id=' + yt.getConfig("SWF_ARGS")['video_id'] + "&sk=" + yt.getConfig("SWF_ARGS")['sk'] + '&t=' + yt.getConfig("SWF_ARGS")['t'];
More information about this bookmarklet, please visit Google Chrome Bookmarklet: Download YouTube Videos in Google Chrome (JavaScript Plug-in).
If you have any questions or advices about this bookmarket, please leave your comments.
Update: Download YouTube Videos in Google Chrome