I like the feature in yaf to insert rel='nofollow' in all post links to cut down on spam. However I would like to allow people that truly do participate in the forum the ability to have 'dofollow' links.

Like all links are 'nofollow' until you make 10 posts, then all of your posts become 'dofollow'

Or even do not allow links in posts or signitures until you have made 10 posts.

Is this possible? Can someone help please?

I know this doesn't answer your question, but dofollow / nofollow are really overrated as far as SEO goes, from what I understand.