I agree with most of the comments here, but like most stereotypes, it does not work all the time.
I tend to frequent the same bars year after year and I have found a few the of Mammasans to be very helpful and honest businessmen. A couple have been very helpful in advising me on things to see and do outside the bar. Once they get to know you, they can often be very good match makers.
That being said, going a new bar and having a persistant and pestering Mammasan really puts me off. One drink and I am out of there.