www.keepvid.com or ClickToFlash (though Flash may be needed) does allow downloading YT videos.
I'm not willing to install Flash for this, sorry.
Minor Problems
6. Sequential posts.
Combine your comments into one post rather than making many consecutive posts to a thread within a short period of time.
http://v15.lscache3.c.youtube.com/videoplayback?sparams=id%2Cexpire%2Cip%2Cipbits%2Citag%2Calgorithm%2Cburst%2Cfactor%2Coc%3AU0hPSVRLV19FSkNOOV9MRUFH&fexp=903809&algorithm=throttle-factor&itag=18&ipbits=0&burst=40&sver=3&signature=0D67D3B81049BF7C42101403CB50C5FB8217F50C.5497AFB6D4CC82930CEDC082DF1C5386FFDD0B6B&expire=1304409600&key=yt1&ip=0.0.0.0&factor=1.25&id=5054da5e91720807
When you have Flash installed and ClickToFlash, Flash object will not be executed unless clicked on, thus Flash takes no CPU cycles unless needed.
Btw, to quote someone, just press the Image button.
To quote several posts, use the Image button (multi-quote).
To edit your posts, use the Image button.
All these buttons are on the bottom right of the posts.
Go to Window > Activity. Under the heading for the YouTube page there will be two sections titled "about:blank." Expand the first one, and double-click while holding the option key on the link that looks something like this:
Code:http://v15.lscache3.c.youtube.com/videoplayback?sparams=id%2Cexpire%2Cip%2Cipbits%2Citag%2Calgorithm%2Cburst%2Cfactor%2Coc%3AU0hPSVRLV19FSkNOOV9MRUFH&fexp=903809&algorithm=throttle-factor&itag=18&ipbits=0&burst=40&sver=3&signature=0D67D3B81049BF7C42101403CB50C5FB8217F50C.5497AFB6D4CC82930CEDC082DF1C5386FFDD0B6B&expire=1304409600&key=yt1&ip=0.0.0.0&factor=1.25&id=5054da5e91720807
The mp4 file should start downloading right there. I use the YouTube5 extension and this method has never failed me.