Yes, when I was little younger (in my teens), I was usually pretty competetive natured when out fishing with the buds and bros and such. Now I'm a little older (28) and I am just as happy if not more when a fishing companion is lucky enough to have success. As for sharing flies, tips, secrets with fishing compainions...I'll always try to help.
At my extended families annual fly-fishing getaway we have prizes for biggest fish and smallest fish, including released fish, although a highly sought after prize in our highly competetive ranks, everyone is happy and proud of the winner 'cause getting to spend time with friends and family and fishing at the same time is what we are really there to do and enjoy.
As for sharing knowledge with complete strangers...I guess it depends on you, personally I have no problem helping seemingly nice strangers without giving away too much. There's lots to be learnt from others, sometimes some simple observation is just as effective.
I guess the saying can be applied to fishing in a way..."a good magician never gives away his secrets"
I'd say a good fisherman never gives away ALL their secrets.