"The 1990 CEC allows one exception to the grounding problem: you can substitute a GFCI outlet for an ungrounded outlet, because a GFCI behaves as though it is grounded,even if it isn't.
A GFCI contains a hole for the grounding prong on three-prong plugs.It is particularly useful when you want to upgrade an old two-wire electric system that doesn't have an equipment ground. You get safty at a bargain price. Paying about $10.00 for a GFCI outlet is a lot cheaper than tearing open walls to run new wiring"
This information is on page 85 of The Family Handyman-How a House Works by Duane Johnson/consultant Jon Eakes
I have replaced the outlets in my own house with the GFCI's and I feel much safer with them. I paid $10.00 canadian for each one.