After it was offered on HSPA, some users pressed their luck and got into several gigabytes. I wish that I could find the original thread. You might want to scour this one: http://www.howardforums.com/showthre...lling-SIMs-now . The issue was in the past by the time that I mentioned it here: http://www.howardforums.com/showthre...unlimited-data! .
Basically, if you are an habitually heavy user, I would say that you should expect some blowback for consuming many gigabytes. It's clear from their offerings since discontinuing the unlimited option that PC Mobile and Bell were only thinking about feature phones with consumption of less than 100 MB/month. They probably figured that they would minimise costs by not even doing the billing per megabyte. That doesn't mean that they don't measure it behind the scenes.
I typically consume less than 1 GB/month, but it might have gone over that from time to time. I have never had any issues with the unlimited option, whether it's the $0.25/day version or the original $5/month version.