Well I'm stuck in the departure lounge for the next three hours, so I thought I'd post a quick update. The journey here was pretty painless, to be honest. Easy train journey to Paddington, easy trip on the Heathrow Express, job done. Actually, the Heathrow Express is cool. Nice big train, and fun music that to my mind was all adventure-y, and it kicked in just as the train was starting, which was good.
On the less good side, it would transpire that I've managed (somehow) to forget my letter of employment, which means that there's a chance that I could be turned away at immigration. And I can access it online, but there's no printers in the departure lounge, or anywhere in the airport for that matter, so I can't print it off again. Also, despite being certain that I'd put it in my hand luggage, my watch seems to have been left behind as well. The one item I was told to bring at all costs. I guess I'll just have to pick up a cheap one in America (provided I get let in!).
Anyway, that's about all for now, so I guess I'll be heading out to have a look around duty free. For three hours. Joy.