All depends on your running style... I'm certain that more people than we realise will just buy any running shoe and run without problems, others will suffer terribly unless they have the correct shoe.
When I started running I hust bought a shoe that was on offer and was 'recommended' by the guy at JJB. I was fine running in these shoes until I started to train more regularly and began to suffer with shin splints. Since then I've had my gait assessed and invested in shoes to correct my overpronation. I'll soon be looking to have my gait assessed again at a proper running pace (first time round I was assessed whilst jogging at about 9kmh - a pace which I would never run at on the roads now; and I'm sure one's gait changes slightly with pace)