It might be fun to F with godaddy.com and start pumping them randomly with domains. Mixing random words in the dictionary and trying combinations in sequence like a typical user would would be effective.

Set this up to happen on a daily basis through proxy servers for different ips, and you might create an interesting way to bleed them a little bit.

Record the domains entered, and see how many times you get them to nick you. It would make for a fun blog post.

Keep in mind, they have to pay ever time they register a domain.