I went to the "London Prepares" series of events eariler this year an attended events at the North Greenwich Arena (Gymnastics), the Aquatics Centre (Diving) and the Velodrome (Cycling in case you don't know what a velodrome is!)
At the Dome, there was no more security than on a normal concert night, ie, all bags searched, pat downs if selected.
At the Olympic Park, they were very quick in scanning everyone. For the Cycling we took in a packed dinner (M&S) and 2 frozen water bottles of 500ml each. It was 28c inside! There were signs up saying 100ml limits, and people were emptying them before security, but we didn't get pulled up on it. On the night of the Diving we actually ate at Stratfield (Stratford Westfield) as there's more choice there than what was open for the trials, and also cheaper!! Yes, it may be event pricing, but that's no reason to gouge people.
I've only managed to score tickets to events in the Excel centre for the Olympics so it will be interesting to see how they cope with the security there. I'm back at Olympic Park for the Paralympics and for each even I'll be getting there early to get through security etc. Patience is the key.