First of all, I love this site. I've already spend over an hour reading the questions and answers!
I'm going to be travelling to Boston (don't know when or the aircraft type yet) and just wondered whether they fly near land, ie Iceland/Greenland/Canadian coast, etc or whether they just fly straight over the Atlantic?
I'm a very nervous flyer and I tell myself that they stay near land so they can make emergency landings etc?
Your flight to Boston will either be flying over the Atlantic or nearer to Greenland. It all depends on the prevailing weather conditions. The airways change daily to take advantage of the jet streams or to avoid some bad weather system.
I have flown across the Atlantic many times on the Boeing 777 towards New York (routing close by to Boston) and most of the times we were given the Iceland-Greenland-Canadian routes, but on the return leg, it was mostly over the Atlantic.
Even though the plane may be flying over the Atlantic Ocean, many airports along the way (eg, Shannon, Keflavik, Stromfjord, Hallifax, St Johns, Gander) are nominated to be used as emergency landing fields should the need requires it.
So there is no fear that you would be too far away from the land