I heard a rumor Pax is going to be on the same day as Anime Boston and there is a combo pass you can get to get into both. With this rumor I heard they will have shuttle service to move the nerds to and from the two cons.
Well, the two cons are the same weekend. That isn't a rumor, that is a fact.
A combo pass, or shuttle service are just rumors for now. Robert Khoo from Penny Arcade said that they'll try and work with Anime Boston to help them in anyway possible, including giving them free booth space to sell passes from Anime Boston at PAX, and trying to coordinate shuttle service. As of now, I haven't seen anything worked out between the cons, other than they want to make it work.
It's also Easter Weekend next year.
Here is the thread from the PA boards where Khoo jumps in and talks about the date selection and wanting to work with Anime Boston.http://forums.penny-arcade.com/showpost.php?p=18678526&postcount=34