They changed from doing them twice a year to once a year, so if 49 is May 2013 then the 50th will be 2014. To be honest, every weekender has an amazing line-up so I wouldn't specifically wait for the 50th party. May 2010 alone had Carl Craig, Derrick Carter, Dixon, Spinna, Grandmaster Flash, Karizma, Kenny Dope, Kerri Chandler, Roger Sanchez, Theo Parrish & Todd Terje + Beverley Knight, Naughty By Nature & Sounds Of Blackness live.
Think next May is nearing a sell-out and they only have certain accommodation options left though.