I've noticed that there has been many cross-over episodes involving One Piece and Toriko.
In fact, Toriko's first episode has One Piece characters in it.
Is there any kind of connection between both of the two series?
Some possible reasons:
anime info: http://www.mahou.org/Showtime/?o=ET
manga info: http://en.wikipedia.org/wiki/Weekly_Shounen_Jump#Series
Year later at the 1st anniversary of Toriko and because of the success of the first collaboration, a second Toriko x One Piece Collaboration Special was announced. A 1 hour special serving as Episode 51 of Toriko and Episode 542 of One Piece.
A third collaboration special crossover was aired on April 7th, 2013, titled Dream 9 Toriko x One Piece x Dragon Ball Z Super Collaboration Special. A 1 hour special featuring characters from Toriko, One Piece and Dragon Ball Z and serving as Episode 99 of Toriko and Episode 590 of One Piece.
There are so many collaborations between Toriko and One Piece because both manga-ka, Eechiro Oda and Mitsutoshi Shimabukuro are very good friends and rivals and they decided to make a crossover seens both manga are serialized on the Shonen Jump :D