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OK... you say that you have.... -- GREAT domain -- Great rankings -- Valuable keywords -- Tidy link profile -- horrible website That gets my blood pumping...  I would be sniffing this site to see if I can do these... -- improve the SEO and triple the traffic -- redesign the site and make it twice as easy to use and double the conversion rate -- create new content to make it more credible and go after new keyword that will double the traffic -- reformat the product pages and double the income -- so, after you triple the traffic from SEO, double conversion rate, double the traffic with new keywords and double again with better product pages.... this site will be making a fantastic amount of money This, to me sounds like a candidate for a flip.  A 301 redirect might be selling a champion racehorse for horse meat. If this site was under my nose I might be grabbing it and taking away the sales from everyone else in that niche. (No guarantees on the above... depends upon the attributes of the site you are starting with, your skill set and how hard you are willing to work)

Whilst I do agree with Federico, it is also possible to 301 those old sites to the new one and enjoy about 85% of the linkjuice they had. There are perfectly legitimate reasons why one might do this - indeed I once closed 4 separate websites and 301'd them to my new site in order as the business we being consolidated. None of this was about building a private link network at the time...that's just how it worked out. Anyway, my new site went from PR0 to PR3 at the next toolbar PR update and has been fine for 3 years+ Just my 2 pence...

The blog network (link juice farming) is against Google's Editorial Guidelines. You never know if you'll get caught, but many people have. Link juice farming on product/client specific blogs, or focus on content for each course niche on main site, that is the question?! Focus on content for each course niche on the main site. Blogs tend to have higher bounce rates, but if that is a concern you can filter out (EXCLUDE) your blog to see what you real conversion rate is in Google Analytics. As far as conversions, it will depend on the purpose of the blog: sales, leads, newsletter signups. I would only have one blog because you can build a lot more authority with one blog than splitting up the blog five ways.

my take from my experience: if you are already ranking for that key term, then you redirect it to a related topic, you'll rank on that spot within a week. lasting on that position is a different story especially if you stop linking. You can drop within a month or 3 months down the road or you can stay put for years. Not really something I can predict as it is a keyword to keyword, niche to niche basis.

We did just update OpenSiteExplorer this afternoon, but I believe it is fully rolled out with updated data. We don't have the number of servers that Google or Bing have, and we're not able to crawl as deeply as they do. That said, we do try to crawl the most important links on the web, and provide metrics you are not able to get from the search engines. We update OSE about once a month. We have more information about the index in this afternoon's blog post at http://www.seomoz.org/blog/november-mozscape-index-is-live Hope this helps!