What exactly is Boxing Day? Is that when presents are opened? When the boxes are discarded? When you take the boxes back to the stores because you don't want what's in them? Are there boxes? Yes, I put too much thought into this!
I'm not sure where the name Boxing Day originated from, but it's simply the day after Christmas. Here in Canada it has become a lot like the Friday after Thanksgiving in the States, with big sales and crazy deals at the stores, but that's a more recent (last 20 years?) development. In Ontario, where I live, it's a statutory holiday, so most offices and public services are closed, but retail stores, restaurants, etc. are open for business. In my family it's just an extension of the Christmas holiday -- when I was growing up we saw one side of the family on Christmas day and the other side on Boxing Day. Oh, and the most important part? Hot turkey sandwiches for lunch. Very important.
Some more information: http://en.wikipedia.org/wiki/Boxing_day
It's not a statutory holiday in other provinces (including mine) but IME the great majority of people in 9-to-5 type jobs do get it as a paid day off. It would be pretty hard for them to conduct business if they remained open anyway. People who have to work don't get holiday-pay, however. I've never been a Boxing Day shopper myself - I hate crowds, no matter how good the deals might be. And the ads can be pretty deceptive - an electronics item could be priced at about 80% off, but the fine print says something like "limit of 4 in each store". One of my DSs lined up in the middle of the night once and said, never again.
Re metric: us Canadians really can't make up our minds. Distances: most of us have gotten pretty mainstream with metres, kilometres, etc. Weight: when talking about body-weights most of us still refer to pounds, although doctors/hospitals use kilograms. Meat/deli items are sold in metric, but some stores will print Imperial in smaller print. Canned foods are technically metric, but in weird sizes such as 298 ml. Cooking measures: I dutifully bought a set of metric measuring cups/spoons when the conversion was supposed to happen and have probably used them maybe twice. Most of use still use "old" Imperial recipes, and many recipes off the Net (such as American ones) are of course Imperial anyway.