Hmmm I walk to my main grocery store. Though its a T&T and not everyone could find what they want there. There are enough plazas around that the distance to one in Mississauga wouldn't be much different that distances you'll have to walk in residential areas of Toronto like North York, Etobicoke, Scarborough etc.Transit in the GTA has gone nowhere in the last 15 years. Its all built on the assumption people commute to downtown Toronto. However job growth in downtown Toronto has been zero over the last 15 years, and its ballooned everywhere else.
I was born in Toronto and grew up in various parts of the Greater Toronto Area. I too love southern Ontario and the fact that my friends and family are almost all here is a huge plus. The ethnic diversity and amount of things to do here are huge pluses to me. My boss wants me to re-locate to the Raleigh, NC area where I spend about four weeks a year but I've managed to keep my job without having to do so thus far. Of the places I've visited or lived briefly I could see myself moving to some coastal cities like San Fran, San Diego, Boston or NYC if an excellent opportunity comes along. There are a few cities in Europe I would definitely consider relocating to for the same reason.
I don't think Toronto is about to go bad, though its certainly not the city it had the chance to become since it sold out its waterfront to condo development. I lived/worked there for 5 years but I find I prefer driving, living and working out in "the burbs" if you can still call Mississauga that at 700,000 people and a net importer of workers now.