Youtube video related

youtube_video technique
Download YouTube Videos the Easy Way
Set videos playback to the lowest definition

Unless the link explicitly sets the playback quality to something higher, it does play back the lowest quality by default. I suspect, however, that the lowest quality is not a low as it used to be. Certainly older clips still look horrible and have lower resolution, but newer material doesn't seem to be encoded at the the old rates and resolutions because, well, they were crap.

• Log in to YouTube, go to the playback settings and select that you have a Slow Connection.
• en.wikipedia.org/wiki/YouTube#Quality_and_codecs
• By adding the parameter fmt to the URL. See http://en.wikipedia.org/wiki/YouTube.
  Google can help you find GreaseMonkey scripts that do that automatically. 
• Add &hd=0 to the YouTube URL. That will display the video in 360p.
  Ex. http://www.youtube.com/watch?v=nxdtVWvfFSU&hd=0
  Additionally, you can add $hd=1 to the URL to get 720p (if available).
  Ex. http://www.youtube.com/watch?v=nxdtVWvfFSU&hd=1
• &fmt=18 is generally lower quality than the default 360p version.
  The lowest quality is &fmt=5 (flv1/mp3, 350 kbps).
  A script for &fmt=18 http://userscripts.org/scripts/show/24980
• The lowest quality is &fmt=5 Seems to work - didn't know about that trick. I tried it on the video below. File size is about half the 360P version. That measn there are now five versions of some videos?
  If you upload the video in the correct format, you can get five versions of a video
  360P/480P/720P-HD, 1280P-HD, like this video HERE. And apparently a fifth version using the tag above.
  I've always assumed that youtube throttles downloading of all their videos.
  For me, they always start downloading fast, then throttle back after about 25%. 
  They probably keep the &fmt=5 version for users with older versions of adobe flash player that don't support h264/aac.

www.google.com/support/forum/p/youtube/thread?
userscripts.org/scripts/search?page=33&q=YouTube