A site hosted on the .mobi domain name will be optimized to be viewed on a mobile device such as a cell phone or a blackberry. When you access a dot-mobi site, it will load faster and look sharper on a mobile device.
The dot-mobi domain is currently open for registration for trademark names, and will be open for public registration on August 14th 2006. The registration, currently priced at $140USD, is about 14 times more expensive than registering a dot-com domain. This is to help prevent cybersquatting.
It’s rather funny to see all the giants rushing to register their dot-mobi domain names before registration is open to the public. I don’t see dot-mobi as a bad thing as it should help mobile users find content that is easily viewable on their small display.