Making the best HQ youtube movies?

I've made some great video clips I'd like to post on youtube in HQ format.
There are some guidelines available to encode videos in such a way youtube will show them in high quality. (like this one for instance: http://www.youtube.com/watch?v=hLtTNE61iik )

What format/encoding settings would give the best results with a Mac?

I watched that video and the interesting thing mentioned was, if the vertical size was a particular size or bigger, YT would encode both a regular quality and a higher quality video. That is good information to know.

As for your Mac, I wrote a "Preparing Video for YouTube" guide that may be helpful. The short answer is that there is no single formula.

Keep in mind that there are other free services that deliver much better quality, even true 720p HD. See this Macworld article.

I experimented a bit more today and I found the x264 codec working pretty good ( http://developer.berlios.de/projects/x264qtcodec/ ).
I encoded my movies with quicktime pro, with the following settings, all of them showed the HQ option (after a couple of hours):

Export: Movie to Quicktime Movie
Video settings:
compression H.264(x264)
quality: Best
frame rate:30
Bitrate: 3000 or higher (as long as you keep the resulting file < 1 gigabyte)
Frame reordering: yes
Encoding mode: multi-pass
Dimensions: 640x480
Sound settings:
format: AAC
Sample rate: 44.100hz
Channels: Stereo (L R)
Bit rate: 112 kbps (I didn't want better, because we also sell those tunes)
Prepare for internet Streaming (selected) and fast start.

Are you saying you installed that encoder you linked to? Why? Apple has a fine H.264 encoder built-in as seen in my iMovie Export Guide.

If you made the movies in an editor other than QuickTime Pro, why not use that tool to do the export?

I doubt adding the "Prepare for Internet Streaming" adds any advantage, as YouTube would add that in when they convert your file.

Lastly, are you saying you can upload a file larger than 100MB via OS X, or did you use Windows for that?

I tried the standard encoding, but it had slightly worse results.

The webinterface allows you to upload files larger than 100mb with osx. The files I uploaded were between 300 and 700mb.

I'm waiting for some more information considering the best codec/settings, someone with direct contact with the people from youtube is going ask them soon. I'll post the info here once I've got it.