Polzin - yes Concorde may fly over populated areas, but only subsonic. That is why it is actually allowed to get airborne and land again! However, they head off over the southwest of England to reach the Altlantic without having to dealy supersonic flight due to crossing Ireland. These routes also keep them clear of the other North Atlantic tracks so that you don't drop a boom on someone's 747!
Incidentally, as a military transport pilot I have flown underneath Concorde on these southern routes and you can feel and hear the double boom as it passes 30,000' above you.
Mycroft - the Gulfstream tie-up was with Sukhoi who are currently producing some great airframes but there is no sign of the proposed SSBJ yet.