I have done in the past. Don't think it was much better than the other stuff I use. To be honest, I tend to use a mix of systems to analyse a site. For free stuff, SEObook are quite good. You just have to remember that some of these free tools aren't that acurate - alexa for example is only any good if you have massive traffic figures.
I agree that you have to use a mixture of tools. SEO book is not bad. I have tried some which were really poor. Alexa is used by most major SEO's as a way of learning about aggregate scoring (ie page views over page visits). I use it to identify percentages of difference between one client and their competitor. I know that the stats are actually only from people who have Alexa toolbar installed, but there are millions of them now so it pays to understand and take note.