The only thing I would add is that a domain can never have more than 10 years on it. So if you created a domain today with a 10 year period and decided to transfer it in 3 months it wouldn't get a year added to it when you transferred. Note that the year is not actually added to the domain by the registrar. It's part of the way the system works for .com .net domains with Verisign which operates the backend for <b>all</b> registrars.
