There are three kinds of PR going on. The first is pure author publicity: The Times columnist Simon Jenkins gave a terrific slide show about his bestselling Penguin books on England's finest churches and houses - and promptly signed and sold all the stock in the site bookshop afterwards.
The second type of PR is the festival's marketing. Association is proving hugely successful for Orange, The Guardian, Channel 4, the BBC and others.
Orange has created a chill-out zone where festival-goers can leave their phones to charge while they go and hear the likes of John Updike, Bob Geldof, Joan Bakewell, Germaine Greer and Jung Chang speak.
In corporate terms, the third kind of PR might be called 'internal communications'.
It's the talking and thinking that people do with strangers and friends alike. Novelist Deborah Moggach said she came 'for the buzz'.
Asked about the success of Hay - 70,000 people from around the world converge on the town annually, come rain or shine - The Guardian literary editor Claire Armistead told me: 'People want to talk and exchange ideas; books have a role in bonding people.'
Every talk, reading or debate is followed by questions and comments from the floor. It's usual for discussion to spill out of the tents and into the cafes and bookshops.
When Harvard professor of human rights Michael Ignatieff was delayed, the festival's legendary director Peter Florence distributed boxes of cherries. People's reactions were suitably Hay. 'Ah, you're keeping us sweet,' said one person.
'No, they are trying to get us stoned,' said another.
Whatever. Hay is nicely mind-altering, and if you're quick you can go this weekend. Kate Nicholas is on maternity leave.