Agreed, but if someone has 10,000+ links with 90% keyword will start seeing some changes. I'm sure with someone having 30-50 links its no biggy, but google seems to be looking at the human sides of things. But Best option!? EXPERIMENT!!! lol. Im at work so I cant even find that youtube video. Ill check google quick to see if i can get the link from there................ ok phew , i was able to find it www.youtube.com/watch?v=0aHknOVK-zQ , check it. very useful stuff
My own guess is that something in the region of 40%20%20% for my primary keyword with the rest quite widely spread. Also important to remember that regular white hat SEO will mean that just the URL should also appear frequently unanchored - that's just natural.