Yeah, I met a mate who lives in Trinity College, and I went to a couple of their parties (PARIASIO! MAKE SURE YOU GO). Where he lives, it's very homely due to a smaller house setting, with only 2 stories and about 15 people. There isn't a common room in his, but I would imagine there is one in other dorm areas. It is very convenient to live on campus, and you've basically made friends automatically by being in close proximity for a long period of time (unless you act like a douchebag

). However, this doesn't come for free. He pays 26k for this year alone, and he has no idea what he's going to do next year because that was all his savings, because he moved down from Sydney. Also, I met his friend in 2nd year, who, from excessive partying from College, got 18 for Finance 1 and 30 for Intro. Microeconomics. That's not an exaggeration either, but he wasn't the sharpest knife in the draw.
Pros: Awesome Uni Lifestyle, parties, chicks, alcohol, convenience for club nights in the city
Cons: Costs a shitload, and may be detrimental to grades depending on the person.
I'll be living on campus in the US next year so I'll be experiencing College life, and I think that it is an important aspect to the Uni experience. So I'd recommend you do live on campus, only if you're absolutely loaded. There are cheaper accommodations around the city that are close to uni but don't provide the same 'feel' as the colleges do.