I'm living in Ontario, Canada. I have ordered parts from PartsShop a couple times in the past and I must admit that some parts are cheaper - but not always. When I order parts (or anything else for that matter) from the States I have to add the cost of the following; exchange rate (~ 1.62), shipping, GST, duty and anouther charge for which I've forgotten... something to do with a courier crossing the boarder. So in some cases it's cheaper for me to drive to the MB dealership or parts store and buy locally. I just looked up the price for the distributor rotor on Fastlane $30.60 US - thats $49.57 CND. I was chaged $52.35 CND from the dealer.
Believe me, when I shop online I look everywhere for the best price on everything from book, computer hardware, stereo equipment, and yes, even car parts
A note to any Canadians reading this post... if you order from the US ask nicely for "Gift" or Tractor Parts" to be put on the customs label... no duty or GST ;P
Cheers for now