I don't pass a Semi if I'm going to be stuck beside one for a length of time. I stay aware of their blind spots.
As an ex semi driver and a new motorcycle rider, I can say it is a great idea to NOT ride beside a semi for any longer than you have to. If you are passing one, put the throttle into it and get it behind you quick.
Believe it or not, the wind on the interstate is felt as much by the big trucks as it is by motorcycles. Wind will push a semi around pretty easy.