Some crew do think SBY's are a day off and moan when they are called but in my experience the vast majority of crew understand that we are not calling them out just for the fun of it and it is because we need to crew a flight!
Where I used to work we had a very good relationship with the crews so that helped I think.
As has been said there are no regulations governing how many SBY's you can have, it is all down to the individual airlines.