I just became a bit.ly Pro user - here's some information about it.

The bit.ly URL shortener is known on most of the Internet. Bit.ly Pro (beta) is available for free. Bit.ly Enterprise costs $995/mo. The diferrence between the standard bit.ly and the pro version is an ability to track one domain and use your own URL (the blog uses kwpl.tk). The enterprise version adds tracking multiple domains, branding, suppport etc. (check the image for details). You can sign up for the Pro on bit.ly Products page. When you'll qualify, you'll receive a message about that.