Bruce Lee's Training in Wing Chun:

Bruce Lee had 4 years of training in Wing Chun from between 1954 and the
end of 1958.  2 years was formal education from Yip Man (the undisputed
Grandmaster of Wing Chun) and the senior instructors at the school
(Leung Sheung, Lok Yiu, Tsui Sung Ting, Wong Shun Leung and William
Cheung).  According to Jessie Glover, Bruce's first student in the US,
in his book Bruce Lee: Between Wing Chun and Jeet Kune Do, Bruce
attributed his rapid growth in skills to the great personal attention
William Cheung and Wong Shun Leung paid to him.  William was Bruce's
good friend and running partner at the time and had been the one to
bring Bruce to Yip Man.  Wong Shun Leung also saw great promise in Bruce
and spent time with him. 

In 1956, Bruce was kicked out of the school due to political reasons. 
Wong Shun Leung had already left to start his own school and Bruce went
to train there for a year, also getting together with William when the
latter could get away from Yip Man's place on the weekends (where he was
living at the time). 

In 1958, Bruce left Wong's school and went on almost week long
sabiticals to William Cheung's home (William had now moved back in to
his parents home in the New Territory's) and trained with William for
the year until they both left Hong Kong. 

On subsequent trips to Hong Kong to visit his family, he would pay his
respects to Yip Man.  On these occasions, Yip Man would show him various
things.  Jessie mentions that the last time he went to Hong Kong while
still living in Seattle, Yip Man had shown him some of the Chi Gerk or
sticky leg techniques for example. 

All in all, Bruce's formal training stopped with the Chum Kil form and
half the wooden dummy form.  However, his skill was great enough at the
time he left Hong Kong that he considered himself the sixth best person
in the clan and the only people who gave him problems were the people
who were then considered the best fighters of the clan (according to
what Bruce told Jessie), William Cheung and Wong Shun Leung.  And of
course, Yip Man.  Bruce had stated that at the time he left Hong Kong,
he could hit William and Leung once for every 4 times they hit him. 
Bruce also reported that later in subsequent trips to Hong Kong, he was
throwing Leung around at will. 

He also later mentioned that he felt he could get in on Yip Man during 
Chi Sao, however he held back out of respect.  Consequently, Yip Man 
got upset at Bruce not taking the opening and proceeded to "thrash" him
about the room.