The ideal world would be one of anarcho capitalism. The next best option for libertarians is a classical liberal society in which governments would be restricted to providing defence against domestic aggressors (requiring a police force - localised, not national), providing defence against foreign aggressors (requiring military forces) and some sort of court system (with the emphasis on restitution to victims).
Given that we do have governments I accept that it's reasonable for political leaders to get together now and again to discuss matters of mutual interest. It would be nice to see a group blog - www.G8leaders.blogspot.com - on which the head honchos would pontificate and we could comment, but I don't expect that too soon. So yes, it's OK for the G8 leaders to meet in the flesh. The trouble is of course that every nutter in the world has jumped onto the anti-G8 bandwagon and it seems highly likely that a great deal of damage will be done to property and possibly persons when the demonstrators hit town in July. Certainly, I shall be removing my car from its outdoors parking spot near central Edinburgh on the day of the big march. I seem to recall a spokesman from the Lothian and Borders Police "welcoming" the demonstrators, as has Gordon Brown. But the Chief Constable and the Chancellor won't have to pay for any damage done to "their" property because police stations and government buildings don't actually belong to them. On the other hand, the poor old businessman in Edinburgh (and in Perthshire) faces potential ruin if things get out of hand. There will be no marches demanding that his resulting poverty be addressed by politicians.
I believe that the huge expense being incurred is an outrage. If the eight leaders wish to get together (actually it's nine - the EU gets to participate too) they should do so in some isolated and defensible spot: perhaps Antarctica or Rockall. Alternatively we could give the North Koreans £10 and hold the event in Pyongyang.