I upgraded my WordPress.com blog to a custom domain because I had wanted to upgrade to a custom domain since November 2014.  I researched the benefits of a custom domain and the pitfalls, and everyone’s advice was clear cut – “do it, it will improve your SEO ranking.”  SEO (Search Engine Optimization) is really important to me as something like 90% of my traffic comes from Google.  Only now it’s taken a hit, and it’s all because I upgraded to a custom domain.  Here’s what will happen to your site’s metrics when you upgrade to a custom domain:

1. You will lose your Alexa ranking.  Low numbers are good (Google has an Alexa rank of 1):  Mine went from an extremely healthy sub-6 million (and steadily increasing) to over 18 million overnight.  Take a look:

   

   

2. Your backlinks from your WordPress blog will all redirect – but you won’t be getting that link juice or authority for all the SEO work you’ve been busting your ass over for the past year.
3. So you will lose all your Google rankings.  As an example, here’s a before and after picture for the search term “how to get rid of blue circles”:

   

   

4. This means you will lose traffic.  When you lose traffic, it’s just a negative spiral.  My traffic was over 300 views a day two weeks ago, when I still had a WordPress domain; now I’m on a custom domain, I get 150 to 200 views a day.
5. Sites that heavily lifted content from your site to write their own imitation articles will now outrank you in search results, as will sites displaying 10 words before you have to click next, and ones which are a vehicle for Google Adsense.  The blue circles example is just an example – all of my most-read posts have plummeted down the Google rankings.
6. Gravatar will not accept the domain change as a WordPress site, so while you redirect, as far as Alexa and Google are concerned, your new domain is dead to them.  They have withdrawn help/support as well so you can’t contact them and ask them to fix it.  Gravatar is owned by and integral to WordPress.
7. Since Gravatar is how your WordPress Login manages all your backlinks from your comments on other people’s sites (you know, when people click your name and it magically takes them to your site?  That’s a dofollow backlink), you now lose any link juice from comments on sites with a better Alexa ranking than yours.  I lost three of my most important backlinks from this, because there are a lot of big sites (CNN for example) that are powered by Wordpress.
8. People don’t really look at the URL any more.  Half the kids in schools don’t actually know what to do with a URL if you give them one on a worksheet and put a laptop in front of them.  Most of the people using the internet these days have this same level of understanding of computers.  Therefore the main argument in favour of getting a custom domain from WordPress is redundant – they claim your site will improve in search results and get more authority but it’s just not true because they don’t let you change your backlink in Gravatar – just the website URL in contact details – and Gravatar refuses to accept the new domain as a WordPress account – no matter how many times you give them your login details.  As far as Gravatar is concerned, you no longer have a blog (but WordPress knows you do, so auto-redirects from your old URL.  Any redirected links are worth nothing in SEO terms).
9. I worked twice as hard over the last 7 days trying to get more backlinks on non-Wordpress sites (because my WordPress account’s backlinks are now utterly worthless) and while I’ve gotten four new backlinks pointing to my site from upstream (from more popular sites), I haven’t gained a single inch of ground.
10. The internet at large doesn’t seem to have a solution to any of the above.  So I am writing this for anyone else wondering about upgrading to a custom WordPress domain – if SEO is where your traffic comes from, upgrade to a custom WordPress domain at the START of your blog, or don’t do it at all.

Post-Publication Update: After I published this post, I had a hunch. I’ve just checked, and I’m right: ALL of your internal links need manually changing to the new domain name as well, because WordPress doesn’t do this either. I was under the impression that the “technical difficulties” they said my site might have for 72 hours was because WordPress was crawling my site and changing all the links. So all my INTERNAL SEO (the links pointing to other parts of my own website) all also need changing. This is another cause of loss of Google ranking.