Malcom,
I've had one "slimy" rep in my UPS experience - but she quickly moved onto pharamceutical sales.
I know the majority of drivers here (small city), the rep, his boss, and several others in variuous tech and support areas. I've yet to experience an issue with any of them. They also have a "preferred customer" line and our account rep is simply outstanding.
Anyhow, when in doubt - check google!!
http://www.google.ca/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=us+customs+social+security+number+canada
Some interesting links are the first hit - which includes excerpts as well as a somewhat broken link to the actual US law.
You'll also find a link from fedex's site further down, as well as sites of many Canadian companies with explanations as to why they want the SS#.
I personally think it's dumb law, but there's lots of those on the books. At the moment (for us anyway) it's not being enforced. When/if it does, I guess we'll have to do something about it.
I just take issue with broad brush strokes - I feel UPS gets a bad rap here in Canada (and it seems to be due to their import brokerage fees - but that's another thread)
Wade