See also my post on speeding up your WordPress site!
I put a lot of thought in how I wanted to handle my WordPress blog and my SeriouslyTrivial domain name. I decided to pony up the $10/year and do the official WordPress domain mapping instead of doing a domain forward. Here’s why:
Domain Forwarding Only: This just redirects the domain name to the WordPress URL, so visitors and search crawlers still see http://spice3d.wordpress.com. The real downside is that if I ever move off wordpress.com, I couldn’t mimick the old site URLs on my own. The SeriouslyTrivial.com domain is essentially useless as far as search goes.
Domain Forwarding and Masking: Well this gets a little closer to what I want. Visitors and crawlers would see SeriouslyTrivial.com. However, I finally figured out that all masking does is create an on-the-fly webpage with a frameset that contains the “forwarded” URL. In other words, it doesn’t really “forward” the domain. The downside for this method is that spice3d.wordpress.com would still exist and there would be duplication on search engines. I still sort of have the issue of not being able to mimick the spice3d.wordpress.com URL should I later decide to move the site or host myself. Another annoying side effect is that the favicon doesn’t work due to the use of a frameset. (I suppose I could have gotten around this by just setting up a real page with the proper frameset and giving that page the desired favicon.)
WordPress Domain Mapping: This basically makes it like I am hosting the blog myself and just using the WordPress engine. The cool feature with this is that you can make it so the WordPress URL redirects to the domain name rather than the other way around. In other words, for me, SeriouslyTrivial.com hosts the blog and spice3d.wordpress.com redirects to SeriouslyTrivial.com. (Note that by default its the other way around. On the Domains config page, you have to click the “Put blog here” link next to the domain name and WordPress flips things for you.) This feature will put you back a paltry $10 a year, but its worth it I think. (Important: Doing this can mess up mail if you also use the domain name for that.)
Oh also, it’s a little confusing when you first do the mapping. When you try to add the domain name, WordPress comes back with an error that says you have to buy 10 credits, but gives you no way to actually buy the credits! However, the page will tell you how to set up your DNS nameservers for the domain name. What you have to do is first set up your nameservers , then it will allow you to buy the credits. Why it doesn’t tell you this here, I don’t know. Stoopid.
After WordPress can verify you have changed the nameservers (supposedly it can take hours or days, but it only took a few minutes for me), when you try to add the domain again, a link will appear (instead of the error page) that will let you buy the credits through PayPal. After you buy the credits, when you go back to the set up page there will be a confusingly named “Buy” button. Click it and you can “buy” the domain mapping feature using the credits you just purchased. I know it’s confusing, but just remember to set up the nameservers first. The WordPress FAQ is here.