(sorry for the spam -- I figured this would be a good way to reach people who are interested in the free credits)
I've decided to try out the WordPress.com "gifts" feature by running a contest for 15 free credits. You could use these credits to buy a custom domain name, the CSS upgrade or towards buying more web space / more private users.
More information and rules can be found here:
This will be my only post on the subject in these forums.