I did my lvl 1 and lvl 2 this year, but didn't actually become an instructor.
the internship is pretty good, you have to live at staff accomodatoin though, which is ok but not the greatest.
pay is pretty shit (im from aus, our minimum wage is like 15 bucks). for a lvl1 i think its about 9-10 dollars an hour. expect to be teaching children and/or retards.
halfway through the season you will be like `fuck instructing i wanna freeski' but its tough to do that if you are a mountain employee.
bottom line - don't work at the mountain if you don't have to , but if its the only way you will be able to afford a season in whistler, then do it. all my mates who are interns like it. Just wish they had more free time.
partying there is pretty sweet for the first month and the drugs are good!