Making Redirects Permanent
On WordPress.com, you start with a standard WordPress.com domain name for your blog which looks something like this – example.wordpress.com. You then have the option of upgrading to a custom mapped domain such as example.com.
The good news is by setting example.com as your primary domain, all your visitors who try to access your old example.wordpress.com links automatically get redirected to the new domain.
But what about search engines and other services that access the old example.wordpress.com links ? Up until now, WordPress.com would send those services a 302 redirect which would tell them that a link had a new temporary home, and to go index that new link, but to not forget about the original one.
Today we have changed 302 redirects to 301 redirects. A 301 redirect tells search engines the new link has moved permanently, and they can discard the old links.
Why does this matter ? This change should help maintain traffic levels from search engines when changing or upgrading to custom domains, and makes things more flexible for you if you ever want to move from WordPress.com to self-hosted WordPress.
As with anything search engine related, your mileage may vary, and the timing on when search engines such as Google, Bing, and others update their index is not something anyone can predict. We have a short support document explaining some of the complexities involved with search engines that is worth a read if you have any questions.