Whenever you transfer a domain to a new registrar an extra year of registration should be added onto it so if you transfer a domain to us that expires in 2006, it would add another year so it expires in 2007. As long as you continue hosting with us we would continue to renew it yearly for you for free, though. We do that for one domain per hosting account.
Also note that we consider a domain name you register your property and we don't do anything to hinder the transfer of the domain name away even if it means you are leaving our service. We see the big picture and know that treating everyone with respect will result in more return business for us in the future. There are some hosts out there that hold domains 'hostage' when someone tries to move their hosting away, but that's not how we operate.
- DreamHost Head Honcho/Founder