I recently started promoting offers as well. Email submits and Zip submits work well. If you actually try selling a product, stick with ones that cost no more than 10-20 bucks. I do about 5 videos on one account. Right now I got my IP banned for not using a proxy with tube automator (I was lazy and in a hurry). Once I get a new IP thursday when the IP lease runs out, I will be back in action.
I do a little of everything. I try to use keywords in my titles and descriptions and mix them up. You are right a few videos across 100 accounts brings in more traffic than just a few accounts with tons of videos on them.
Just say you have 5 accounts, with 20 videos each. You get 2 of them banned losing 40 videos. That is a huge hit, and you will notice a huge loss in traffic/conversions. But if you have 100 accounts with 2-5 videos on each, and you get even 5 of them banned, you probably wont notice as big of a difference.
I also noticed a trend in traffic. When you first upload a video, you get a nice spurt of traffic. That traffic lasts maybe a day. Then the traffic trickles in. Leave it alone for about 2-3 weeks, and the traffic steadily grows. The traffic starts growing with age.
Right now I use tube increasor and boost each of my new videos to about 10k views. I then create another account with only 1-2 videos. I use Tube Automator to boost those to the front pages of YouTube to get a huge spurt of traffic. I also have accounts I just upload with good titles, descriptions, then forget about.
With only using a few accounts, you are a needle in a haystack. With using tons of accounts 50+ you become the haystack in a barn which is much easier to find.
For those of you who haven't used or heard of Tube Automator, check out my Video Tutorial over it:
http://www.shudogg.com/tube-automator-youtube-video-marketing/
It really as an amazing software that everyone marketing on youtube should have in their toolbox.