I can't wait.
 

I won a prize which was Virgin Atlantic flights to America.
I absolutely, totally, can't wait. I have got a countdown on my computer, it's 130 sleeps to go.
I haven't been this excited since my last trip to the States which was ten years ago (Icelandair, Business Class out :), Economy back :( )
I can't explain why. I have even been looking at airport hotels at Heathrow, and how to get to and from the airport. It's four months away!

I'm 35.

I thought that by now the excitement of travel would have died down a bit :)

Congratulations to your flight. Where will you go in the US?

Just a quickie - LHR - JFK, and then BOS - LHR.

I was going to get the Acela Express between New York and Boston, but I have since noticed that JetBlue are offering TWO SEATS for $129.00 - thats a bargain! Acela is $176.00 for two seats... not sure what to do. Is it a hassle getting to/from the city centres and JFK and BOS?

I'm not an expert on BOS but I believe that the T (aka metro) goes out to the airport. The T is really easy to understand and easy to ride.

In NYC, getting to JFK is a bit more of a hassle. The easiest is to take a taxi - however, this can be expensive, and take over an hour at rush hour. The subway (A train) is cheap but can be crowded, it's a schlep with luggage and the A train goes thru not so nice neighbourhoods, then you have to switch to a bus for the last bit to the airport. From Manhattan, this will always take you well over an hour.
You can also take the AirTrain to Jamaica station and then the LIRR from there into Manhattan (Penn Station) and vice versa. From Penn Station you can easily catch a cab or the subway. Always depends on how much luggage you have.

If OP's very excited, then he should consider US Helicopter out of Manhattan.
IIRC, it's only like $150 or so per person.

I took the Acela once. It is quite nice to leave from Penn Station and arriving at South Station in Boston. From there you can get directly to the Boston airport via the Silver Line. The Acela ride is just smooth. It goes right by the sea with nice views. I realy enjoyed it.

It is no hazzle to get to JFK it just takes time. From Manhattan its $45 by taxi and takes up to 60 minutes depending on the time of the day and where you start in Manhattan. Subway takes about 90 minutes but is way cheaper.

Up to 60 minutes? My personal best (longest), even from the East side, was over 2 hours. Now don't get me wrong, for a visitor to NYC who is not in a rush, I would still recommend a taxi, but as the post above states, it takes time. Since it appears that it will be 2 of you, that makes the argument for a taxi even stronger - ~$60 including tolls and tip for the taxi vs. ($5 for the AirTrain + ~$7 for the LIRR) x 2 + taxi from Penn St. to your final NYC destination. Basically, the OP would be paying a $25 or so premium for the comfort and ease of a taxi. Well worth it IMO.

Bus from Grand Central
 

It's been 4 years since I was last in NYC, but I've always taken the Port Authority (?) bus to either JFK (about $12 pp) or LGA (about $8 pp) from its location just across 42nd street from Grand Central Station by Park Avenue. Time it takes is about 1 - 1.15 hours to JFK, and 45 minutes to LGA, and the bus makes all the stops to the various terminals. Don't know if this service is still there, but I would guess so since I have been doing this for well over 20 years . From the airport, it's the same in reverse.

This method is very convenient if one is staying at the Grand Hyatt or nearby walking distance hotels, and you don't have a whole lot of luggage.

Thanks so much for the advice.
As part of my prize, I get limo transfers between JFK and the hotel. :D so that actually won't be so much of an issue.

My companion is not a happy flyer, and I wanted to try First Class on Acela. But those JetBlue fares are something else!

Congrats! Obvious reasons to justify your excitement. Just make sure you keep everything under control and don't let that excitement go overboard and affect your daily life before and then the trip. :)

Oh I know. I have to be mature about it. ;)

I second the opinion that the T is pretty easy getting around and understanding, either from Logan or South Station.

Not sure if you have seen this before but someone made a mashup of the T routes using Google Maps. Nice because you can pan and zoom.

Congratulations on winning your trip, have fun! :)

If you haven't been to BOS before, IMO be sure to try Pizzeria Regina and Boston Chowda. Those are two of my personal informal favorite places to eat in BOS.

If you want to go cheap between BOS and NYC, take the chinatown bus for <$20.