It's really calmed down since Heysel and Hillsborough. The chanting is similar, but the fighting has really been clamped down on. The only place I'd be scared as a Gooner to go to would be Italy and Donestsk because the Ultras there are a little off and I really don't think the cops their are as proactive to handle stuff like that. Plus the Racism in Italy and parts of Eastern Europe and parts of the Balkans is way out of control. Besides that, the Home Office even spies on known Hooligans and breaks up potential fights at pubs, neighborhoods and other off site locations if you are in the UK.
Also if you wear a kit or a scarf or any club gear to the game, your are pretty much off limits to "true hooligans".