i have been using YUI 2.0 reset-fonts-grids and base for years as the foundation of my web sites css and I am fairly well-versed in it. I found this question and evaluated blueprint, and it is fantastic, very easy to understand and implement. that said, i would stick to yui reset-fonts-grids and base as my css starting point because I have spent time learning it, and i already have several sites, including my own designed around it. In terms of being able to achieve a layout, I would be able to it faster in YUI right now. A person who knows blueprint would be similarly be able to achieve complex layouts too. Which means, pick one framework and invest time in learning it. There is no difference in the rendered page.
Using frameworks of any kind is advantageous for newbies as well as for experienced people. Frameworks reflect years of experience and get you on a running start. In the particular case of CSS, learning a framework would be far simpler than learning CSS itself, with all the quirks and browser compatibility things. I disagree with bobince on that count. I would prefer to drag 100s of rules written by people who know CSS, and verified by hundreds of others, for just getting 3 columns, than risk writing 3 css rules which make all the mistakes a newbie could make.