As an online gamer and a founder of a gaming community I will be keeping the 360 and purchasing the XboxOne. I have never traded in a system ever, but the design specs for the XboxOne has made it crucial that I keep both.
Gamers who chat on the 360 will not be able to communicate with those that own the XboxOne. This was intentional by Microsoft and a needed evil with the addition of Skype to the XboxOne.
Furthermore, if history is any indicator, gamers will benefit for 1 year with games being made for both consoles. But after a year developers will only design for the newest system. Furthermore, games that get delayed in production, usually get redesigned only for one generation.