A few more comments from me
Swim - yes the wave start meant that i didn't get bashed at all, and in fact felt like I was on my own most of the time. It was bloody freezing though, so two swim hats may be a good idea. Apart from cramp I had no probs getting out of the water as there were plenty of helpers.
Bike course : as Bedders says its undulating (approx 1500ft of climb per lap, and 3 laps for the full distance), the road surface itself is very poor, and there was not much warning when approaching some of the tight turnabout points. The feed stations and marshall were fabulous and cheerful.
I have read that the bike course may be changing for next year though, as there have been compaints from the locals.
Run : it's a combination of road /towpaths and off road, some of which is a bit stony/gravelly underfoot. Plenty of crowd support through Henley, but once you're out on the run loop it's quiet apart from the feedstations.
For the Half-Arsed there is no cut-off time - and I think the last finisher was 8.50ish - they only ask you to let the Pro's doing the Full have their moment of glory if you're finishing at the same time. Although the cut-off for the full is 16 hrs, the last finisher was 17 and a few minutes, so they don't seem to pull you off the course.
oh, and be prepared for any type of weather!