I talked today to someone who went and really enjoyed themselves (smoked salmon sandwiches and strawberries and cream in the Mayor's tent!) The security at the entrance is apparently pretty thorough, but no obvious police presence inside and no trouble - a very relaxed atmosphere, in fact. Lots of worthy voluntary groups setting out their stall.
When I've worked it in previous years the police presence inside was limited to the stalls thay they set up for public information and enjoyment, a couple of senior officers having cups of tea with the great and the good one serial of 6 officers to wander about.
It's outside that the police have "riot gear to hand" as the security is tight enough to prevent any trouble inside the event itself.
That said, i am unaware of any significant disorder this year though (outside or inside the event) which is very good news.