I don't recall seeing this discussed elsewhere so...
According to a recent professional development seminar attended by two of my partners, when you buy a used bike, the total taxes that you pay under the new HST rules should work out to be the same as under the old PST / GST regime.
Under the old rules, if you buy a bike privately, you only pay 7% PST upon registration but no GST. If you buy from a dealer, you pay GST on the invoiced amount + PST upon registration.
Under the new rules, if you buy from a dealer, you will pay the 12% HST. If you buy privately, you will pay only 7% upon registration.
YMMV so please discuss with your own tax practitioner.
Please debate the fairness, or lack thereof, regarding any taxes somewhere else. I'm just trying to inform you of the mechanics of the taxes here.
As usual, E&OE