our site has around 200,000 pages, of which 90,000 are temporary 'product' pages that are client edited and can last anywhere from a week to over a year. with lots of talk of keeping link value and pagerank, we are looking at ways to try and keep value on the upper, permanent parts of our site. some ideas that have been suggested are: to restrict the entire 'product' directory using the disallow command in robots.txt to make all direct internal links to the 'product page' NOFOLLOW both of the above contrarily, there is an opposite line of thought in that we should embrace this temporary content. some ideas are: to make all outgoing links on the 'product page' itself NOFOLLOW, but fully allow internal links to remove the 'product' directory from our sitemap, to try and accentuate that the content is not permanent both of the above we look forward to any thoughts/opinion
NOFOLLOW is your best bet, if you disallow the pages via robots.txt you prevent your clients getting SERP\hits from search engines.
I wouldn't do any of the above. If you the pages are on your site, than you aren't losing any "link juice" just make sure that the product pages have links back to the home and main pages.