Also recommend a trip out West - the usual spots: Salisbury, Bath, Oxford, the Dorset and Devon Coasts and maybe spectacular Cornwall, if time allows.
I will be in London in Aug for one night of the track finals (200m & 800m mens) as the ticket lottery went totally t*ts up and actually gave me some tickets. I'm looking forward to the spectacle but anticipate a nightmare getting in and out of London. For the rest of the Games, the TV is the best bet.
The sailing down in Portland might be worth checking out - all of the viewing tickets are sold I believe (at least the ones offered to the UK public) but I'm sure there will be some free places along the coast where you can check it out.
Bring lots of dosh - UK not cheap, unfortunately. Good luck with the plans !