On the Guild Wars 2 main page today, we finally got the news that guesting is coming. Most notably it will be here at the end of the month. There isn't much else to say about this feature. It will work exactly as it was thought it would. Head over to the Guild Wars 2 main page to read the details.
Don't forget that once guesting is online on January 28th you will no longer be able to transfer servers with out paying a gem fee. Thus, if you are planning on moving servers now is the time to start doing your server shopping.