tangor - 1:13 am on Nov 30, 2011 (gmt 0)

Only publicly visible blogs with custom domains will be considered for this program. If you are interested but don’t have a custom domain, you can quickly sign up for a custom domain for your blog(s) below.

[en.wordpress.com...]
Following the link to sign up for a custom domain indicates:

Registering a domain through WordPress.com and mapping that domain to your blog costs $17.00 per domain, per year. For $8.00 more, you can also make the domain registration private. Mapping a domain you already own costs $12.00 per domain, per year.

[en.wordpress.com...]

If nothing else, WordPress will see some new revenue before any advertising is presented.