Jim - Lons has it in a nutshell - there is not a bandsaw nor a blade in the world that cuts straight, they all drift. The only difference is that a cheap and nasty blade may drift more than a more expensive one.
The excercise in Lons' video is something you have to do every time you change the blade. The only thing I would add is that once you've made your freehand cut, clamp the wood to the table rather than draw a line, then bring up the fence and adjust it to the wood - much more accurate that way.
Phil