I will offer a tip or two, although please bear in mind that I am NOT a cabinet maker and have no knowledge what so ever of the video's subject matter.
1. First of all I think the video would benfit greatly from a multi camera shoot (at least two cameras). I f you don't have two, then script the video a little more, and switch between profile (effectively what you have shot this video in) and head on (90 degrees to your current shot and in front of the speaker).
2. Quality, I actually thought the quality was quite good for YouTube, but I did notice that it takes an earth to load (In fact it didn't stream very well at all). The only thing I can suggest is to try encoding in a streaming format such as WMV. You can download Windows Media Encoder for free (Just google Windows Media Encoder).
3. I thought that the video was rather long, and the speaker tended to jump his subject from time to time. Scripting would greatly improve this.
4 Additionally I didn't really like the transitions (bit home movie like for my liking, but hey thats probably just me). Again a two camera shoot (or 2 position shoot with one camera) would help this as you could do a simple CUT between scenes. Otherwise I would stick to crossfades.
Having said all of that, I couldn't really fault this, it was well shot, well framed and well edited. Couldn't see any significant problems with the lighting. You are right it could be improved, but I would go bust a gut for it, it is fine as it is.
I can see why you have built up a fan base. Well done I say!
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.