Requires SIMBL and GreaseKit. Tested on Safari.

# YouTube in MP4 via QuickTime Plugin!
# http://www.joeyhagedorn.com/2008/04/16/youtube-in-mp4-via-quicktime-plugin

open -a Safari http://www.joeyhagedorn.com/media/downloads/youtubeQT.user.js


# Download YouTube Videos as MP4 Files
# http://googlesystem.blogspot.com/2008/04/download-youtube-videos-as-mp4-files.html

open -a Safari http://members.optusnet.com.au/lbramsay/youtube_mp4.user.js

Youtube QT (http://www.joeyhagedorn.com/media/downloads/youtubeQT.user.js)

// ==UserScript==
// @name           Youtube QT
// @namespace      userscripts.org
// @description    Plays the high-resolution YouTube video in an embedded Quicktime player 
// @version        0.1
// @include        http://youtube.com/watch?*
// @include        http://www.youtube.com/watch?*
// @include        http://*.youtube.com/watch?*
// ==/UserScript==
	
var video_id = null;
var video_hash = null;
var video_player = document.getElementById('movie_player');

if (video_player) {var flash_variables=video_player.attributes.getNamedItem('flashvars');
	if (flash_variables) {var flash_values=flash_variables.value;
		if (flash_values) {var video_id_match=flash_values.match(/video_id=([^(\&|$)]*)/);
			if (video_id_match!=null) video_id=video_id_match[1];
				var video_hash_match=flash_values.match(/t=([^(\&|$)]*)/);
				if (video_hash_match!=null) video_hash=video_hash_match[1];
		}
	}
}

if (video_id==null || video_hash==null) {var args=unsafeWindow.swfArgs;
	if (args) {video_id=args['video_id'];
		video_hash=args['t'];
	}
}

if (video_id==null || video_hash==null) return;

var yt_mp4_path = 'http://www.youtube.com/get_video?fmt=18&video_id='+video_id+'&t='+video_hash;
var div_embed=document.getElementById('watch-player-div');

if (div_embed) {div_embed.innerHTML='<embed src=\''+yt_mp4_path+'\' type="video/mp4" width=480 height=400 scale=\'aspect\'></embed>';
};

// fun with mechanize
// more @ http://tramchase.com/scrape-myspace-youtube-torrents-for-fun-and-profit

agent = WWW::Mechanize.new
url = "http://gdata.youtube.com/feeds/api/standardfeeds/most_viewed" # all time
page = agent.get(url)
# parse again w/ Hpcricot for some XML convenience
doc = Hpricot.parse(page.body)
# pp (doc/:entry) # like "search"; cool division overload
images = (doc/'media:thumbnail') # use strings instead of symbols for namespaces
FileUtils.mkdir_p 'youtube-images' # make the images dir
urls = images.map { |i| i[:url] }
urls.each_with_index do |file,index|
  puts "Saving image #{file}"
  agent.get(file).save_as("youtube-images/vid#{index}_#{File.basename file}")
end