If you are playing in a song circle or a jam session and someone minds you checking out their playing then they have missed the point..playing music together is a very interactive kind of thing and very few musicians would care if you steal a chord or a lick.

Bands that play together alot sometimes will kick off songs in different keys to mix things up a bit. I played in a band where we did this to torment the singers ...kind of breaks the monotony of playing the same set list.

I saw a very old tape of the beatles ca. 1963 where John is banging away and you can see George and Paul staring at his fingers and trying to figure out where he is going with expressions of "what in the H...are you doing John...that's the kind of thing that makes playing music together fun.