Don’t Use Nofollow on Footer Links
John recommends against using nofollow on footer links.
Add Nofollow to Shared Links
If you are giving out links to be shared on other websites, you should ask for nofollow to be added. If a few links are added without the nofollow, it probably won’t cause a penalty, but you can disavow the URLs with the links to be safe.
Don’t Use Nofollow for PageRank Sculpting
John says it’s OK to use nofollow internally to prevent things like a calendar being crawled, but recommends against it for PageRank sculpting and says it won’t change anything.
Googlebot Requires a Consistent Response for Different User Agents
You need to provide the same response for all users based in the US, including Googlebot, or the content might not be indexed.
Google Crawls Repeated Links Where One is Nofollowed
If you have 2 links on a page to the same target, but one is nofollowed, then Google will just crawl the followable link.
Publishing multiple versions of a page on different sites, and canonicalising to a single page for link building, is not acceptable. The duplicates should be nofollowed.
Nofollow Is Ok to Control Googlebot
It’s OK to use nofollow on internal links to control Googlebot behaviour but you need to be careful you are not making it hard for your site to be crawled.
Most Affiliate Links Are Automatically Nofollowed
Affiliate links for main affiliate programs are automatically recognised and effectively nofollowed. They won’t cause penalties.