I've worked at a G7 and a G8 in the past and security will be very tight. I expect that the downtown hotels will be zipped up as tight as a virgin's ass, and that the chain link fence will be going up again. The area around the Convention centre will most likely be off limits. People that LIVE in the Zone will need to be vetted and have passes. If you have an incall in the Zone, you had better think of a way of getting the girls in, and marketing to the G8 people, 'cause no self respecting hobbiest will want to explain to the OPP, the RCMP, CSIS, Canada Command (military), the FBI, the Secret Service, the CIA and just about everyone else who wants to stick their nose in just where you are going or why. If it is like the ones I worked with, expect to be challenged and have your ID checked at least 10 times as you go to where you want to be. If you are allowed in. I don't think "My blue balls need to be released" is going to be accepted as a valid reason to enter the Zone.
Driving will be a total f###ing mess, and even the TTC will be swept for bombs and terrorists, so expect some delays.
If the kiddies want to come to town and play anarchist, it will be a very entertaining afternoon. I guarantee that the security services already know what the kiddies are going to do and have drawn up a number of contingency plans. It is much harder to beat the shit out of the anarchists away from the media spotlight because of the popularity of digital devices.