The USA DTV changeover date is February 17, 2009.

The Candian DTV changeover date is sometime in 2011.

The USA will be switching away from "analogue" transmissions of "Over The Air" Television signals. The reason for this, is that they can save a lot of wireless spectrum (ie: the amount of space available in the sky to transmit stuff wirelessly) by transmitting it digitally. So, you get the same quality signal (perhaps even better) but they can also run things like more data over new cellphone airwaves.

Free Convertors for Americans, But Not (yet?) for Canadians

Anyways, the US government is giving vouchers for its residents to buy Digital TV (DTV) receivers. These can pick up the new signals, and then convert them into something that your TV can display. So, without one of these boxes, once these signals go out, you won't be able to pick them up (if you don't have cable/satelite or some kind of system like that).

Now, here's the problem for Canadians. Canadian stations aren't changing over for a while. But the US ones are changing over on February 17, 2009. So, when that happens, if you live close to the border (or even in Toronto and such) and don't have cable/satelite, you won't be able to pick up those stations (like Fox, CBS, etc) unless you buy one of these convertor boxes yourself. The US voucher/subsidy doesn't apply to you, and there isn't such a program yet for Canadians.

DTV Transition Not as bad as it sounds

On the upside, Canadian TV channels, like Global and/or CTV, often just re-transmit what Fox or CBS transmits. So, for those kinds of shows, you're fine. But if you like watching local Buffalo news, that's a problem. It won't even be possible to switch to antenna/OTA TV during the Superbowl if you live close to the border to watch the US ads (though I never really cared for ads...). And even if you have cable or satelite, during events like the Superbowl, Global/CTV (whichever Canadian does the Superbowl this year) will actually take over the US signal, so the only way to watch the US version is over antenna or some such.

So, just something to watch out for, if you're a Canadian, watch TV over the antenna, and live close enough to the USA to pickup US TV Stations, because they'll go dark without a digital convertor box (which you'll have to pay for yourself).

Since each American that receives OTA signals is eligible for 2 free units, I can only imagine that they'll show up cheaply on Ebay soon enough, if not already.