I won't claim any great knowledge but one of the things i noticed between the two was the 50/50 weight distibution of the the stance. A chueng style SiFu who I am in contact with mentioned that Chueng, Wong Shueng Leung and Lee Jun Fa were known as a very notorious trio. And that the three of them would often have "rooftop" fights with others. He gave this as a reason for the similarities.
There are so many different teachers of Wing chun as well as different lineages that don't even include Yip man it is almost impossible to keep up with them all but I like what I know of the Chueng lineage. I have a couple of months to do reasearch though and am collecting a very nice collection of video clips from the net to learn more.
Tony
Attack, attack, attack -- come at your target from every possible direction and press until his defenses overload. Never give him time to recover his balance: never give him time to counter.
Stover
http://www.members.shaw.ca/tmanifold