For anyone who has read the blurb of Oxford Blood (or indeed, the whole book), and is wondering what on earth a dining society is, here is a very brief guide.
In essence, dining societies are groups, almost exclusively single sex (all female as well as all male, though the girlie ones tend to be much newer and much less well known), that get together to dress up, drink heavily and in theory at least, eat a fancy meal. There are college ones, ones linked to activities, such as rugby teams, and most famously, a few pan-university ones, which tend to get all the attention.
Oxford as a whole suffers from a bit of a reputation for snobbery and elitism. Dining societies get it ten times worse, generally with a lot more justification. In legend, and to a large degree, reality, the members are rich, public school educated and out to cause drunken trouble.
The most famous, by a long, long way, is the Bullingdon Club, partly due to previous references in literature, stretching right back to Evelyn Waugh, partly due to the levels of their excess and partly due to the slightly alarming fact (well, alarming to a lot of people, personally I find it highly amusing) that the Prime Minister, the Chancellor and the Mayor of London were all members whilst at Oxford.
There are however lots of other similar societies. The Piers Gaveston have wild outdoor summer parties with lots of sex, drink, drugs and fancy dress (despite the blurb, they probably inspired the Cavaliers at least as much as the Bullingdon, though as far as I recall no one actually dies at these events).
Some other biggish ones are the Phoenix Club (Brasenose only), The Cardinals (Christ Church) and the Stoics (University Wide).
These societies, the Bullingdon in particular, tend to crop up in the news surprisingly regularly and the stories are always quite amusing, so be prepared for regular updates on their activities on the blog.